refactor(bin): move non-spec root files into references/ across four skills

grill-with-docs, improve-codebase-architecture, tdd, and triage kept
non-spec markdown files at their skill root, in violation of
skill-audit's file-structure.md rule (only SKILL.md/README.md belong
at the root; everything else lives in scripts/, references/, assets/
or tests/). A root-level file is invisible to the ADR-0020
dangling-reference gate, which only resolves unqualified
`references/...` pointers.

- Moved and renamed to lowercase-kebab-case under references/:
  grill-with-docs (ADR-FORMAT.md, CONTEXT-FORMAT.md),
  improve-codebase-architecture (DEEPENING.md, INTERFACE-DESIGN.md,
  LANGUAGE.md), tdd (five files, casing was already fine), triage
  (AGENT-BRIEF.md, OUT-OF-SCOPE.md).
- Updated every in-skill link to the new references/ paths, including
  link text that still showed the old uppercase filenames.
- Fixed improve-codebase-architecture/SKILL.md's cross-skill citation
  of grill-with-docs's two files to the sanctioned possessive form
  with the references/ segment included.
- Updated all four skills' README.md file tables to match.
- Regenerated the flat content mirror via
  scripts/sync-plugin-content.sh --all.

Fixes #122.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PDj6F7SPXzh3FtPN78dZ88

plugins/bin/skills/improve-codebase-architecture/README.md

@@ -31,6 +31,6 @@ Point at a codebase or an area of one. Expect a numbered candidate list and a "w
 | File | Purpose |
 |------|---------|
 | `SKILL.md` | Condensed glossary, key principles, and the three-stage process |
-| `LANGUAGE.md` | Skill-root document, cited throughout `SKILL.md`: full definitions of every term, the words each one replaces, and the full principle list |
-| `INTERFACE-DESIGN.md` | Skill-root document, read at stage 3 when the user wants alternative interfaces explored: the parallel sub-agent "Design It Twice" pattern, framing the problem space, and the per-agent design constraints |
-| `DEEPENING.md` | Skill-root document, cited from `INTERFACE-DESIGN.md`: how to deepen a cluster of shallow modules safely, the four dependency categories (in-process, local-substitutable, remote-but-owned, true external), seam discipline, and the replace-don't-layer testing strategy |
+| `references/language.md` | Cited throughout `SKILL.md`: full definitions of every term, the words each one replaces, and the full principle list |
+| `references/interface-design.md` | Read at stage 3 when the user wants alternative interfaces explored: the parallel sub-agent "Design It Twice" pattern, framing the problem space, and the per-agent design constraints |
+| `references/deepening.md` | Cited from `references/interface-design.md`: how to deepen a cluster of shallow modules safely, the four dependency categories (in-process, local-substitutable, remote-but-owned, true external), seam discipline, and the replace-don't-layer testing strategy |

plugins/bin/skills/improve-codebase-architecture/SKILL.md

@@ -33,7 +33,7 @@ Key principles:
 - **The interface is the test surface.**
 - **One adapter = hypothetical seam. Two adapters = real seam.**
 
-If a term or principle above is ambiguous in the case in front of you, or you need the definitions and the principles the two lists leave out, read `LANGUAGE.md`.
+If a term or principle above is ambiguous in the case in front of you, or you need the definitions and the principles the two lists leave out, read `references/language.md`.
 
 This skill is _informed_ by the project's domain model. The domain language gives names to good seams; ADRs record decisions the skill should not re-litigate.
 
@@ -74,7 +74,7 @@ Once the user picks a candidate, drop into a grilling conversation. Walk the des
 
 Side effects happen inline as decisions crystallize:
 
-- **Naming a deepened module after a concept not in `CONTEXT.md`?** Add the term to `CONTEXT.md` — same discipline as `grill-with-docs`, in the format `grill-with-docs`'s `CONTEXT-FORMAT.md` defines. Create the file lazily if it doesn't exist.
+- **Naming a deepened module after a concept not in `CONTEXT.md`?** Add the term to `CONTEXT.md` — same discipline as `grill-with-docs`, in the format `grill-with-docs`'s `references/context-format.md` defines. Create the file lazily if it doesn't exist.
 - **Sharpening a fuzzy term during the conversation?** Update `CONTEXT.md` right there.
-- **User rejects the candidate with a load-bearing reason?** Offer an ADR, framed as: _"Want me to record this as an ADR so future architecture reviews don't re-suggest it?"_ Only offer when the reason would actually be needed by a future explorer to avoid re-suggesting the same thing — skip ephemeral reasons ("not worth it right now") and self-evident ones. See `grill-with-docs`'s `ADR-FORMAT.md`.
-- **Want to explore alternative interfaces for the deepened module?** Read `INTERFACE-DESIGN.md`.
+- **User rejects the candidate with a load-bearing reason?** Offer an ADR, framed as: _"Want me to record this as an ADR so future architecture reviews don't re-suggest it?"_ Only offer when the reason would actually be needed by a future explorer to avoid re-suggesting the same thing — skip ephemeral reasons ("not worth it right now") and self-evident ones. See `grill-with-docs`'s `references/adr-format.md`.
+- **Want to explore alternative interfaces for the deepened module?** Read `references/interface-design.md`.

plugins/bin/skills/improve-codebase-architecture/references/deepening.md

@@ -1,6 +1,6 @@
 # Deepening
 
-How to deepen a cluster of shallow modules safely, given its dependencies. Assumes the vocabulary in [LANGUAGE.md](LANGUAGE.md) — **module**, **interface**, **seam**, **adapter**.
+How to deepen a cluster of shallow modules safely, given its dependencies. Assumes the vocabulary in [language.md](language.md) — **module**, **interface**, **seam**, **adapter**.
 
 ## Dependency categories
 

plugins/bin/skills/improve-codebase-architecture/references/interface-design.md

@@ -2,7 +2,7 @@
 
 When the user wants to explore alternative interfaces for a chosen deepening candidate, use this parallel sub-agent pattern. Based on "Design It Twice" (Ousterhout) — your first idea is unlikely to be the best.
 
-Uses the vocabulary in [LANGUAGE.md](LANGUAGE.md) — **module**, **interface**, **seam**, **adapter**, **leverage**.
+Uses the vocabulary in [language.md](language.md) — **module**, **interface**, **seam**, **adapter**, **leverage**.
 
 ## Process
 
@@ -11,7 +11,7 @@ Uses the vocabulary in [LANGUAGE.md](LANGUAGE.md) — **module**, **interface**,
 Before spawning sub-agents, write a user-facing explanation of the problem space for the chosen candidate:
 
 - The constraints any new interface would need to satisfy
-- The dependencies it would rely on, and which category they fall into (see [DEEPENING.md](DEEPENING.md))
+- The dependencies it would rely on, and which category they fall into (see [deepening.md](deepening.md))
 - A rough illustrative code sketch to ground the constraints — not a proposal, just a way to make the constraints concrete
 
 Show this to the user, then immediately proceed to Step 2. The user reads and thinks while the sub-agents work in parallel.
@@ -20,21 +20,21 @@ Show this to the user, then immediately proceed to Step 2. The user reads and th
 
 Spawn 3+ sub-agents in parallel using the Agent tool. Each must produce a **radically different** interface for the deepened module.
 
-Prompt each sub-agent with a separate technical brief (file paths, coupling details, dependency category from [DEEPENING.md](DEEPENING.md), what sits behind the seam). The brief is independent of the user-facing problem-space explanation in Step 1. Give each agent a different design constraint:
+Prompt each sub-agent with a separate technical brief (file paths, coupling details, dependency category from [deepening.md](deepening.md), what sits behind the seam). The brief is independent of the user-facing problem-space explanation in Step 1. Give each agent a different design constraint:
 
 - Agent 1: "Minimize the interface — aim for 1–3 entry points max. Maximise leverage per entry point."
 - Agent 2: "Maximise flexibility — support many use cases and extension."
 - Agent 3: "Optimise for the most common caller — make the default case trivial."
 - Agent 4 (if applicable): "Design around ports & adapters for cross-seam dependencies."
 
-Include both [LANGUAGE.md](LANGUAGE.md) vocabulary and CONTEXT.md vocabulary in the brief so each sub-agent names things consistently with the architecture language and the project's domain language.
+Include both [language.md](language.md) vocabulary and CONTEXT.md vocabulary in the brief so each sub-agent names things consistently with the architecture language and the project's domain language.
 
 Each sub-agent outputs:
 
 1. Interface (types, methods, params — plus invariants, ordering, error modes)
 2. Usage example showing how callers use it
 3. What the implementation hides behind the seam
-4. Dependency strategy and adapters (see [DEEPENING.md](DEEPENING.md))
+4. Dependency strategy and adapters (see [deepening.md](deepening.md))
 5. Trade-offs — where leverage is high, where it's thin
 
 ### 3. Present and compare