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/.apm/skills/tdd/README.md

@@ -25,8 +25,8 @@ Describe the feature or bug. Expect the skill to ask what the public interface s
 | File | Purpose |
 |------|---------|
 | `SKILL.md` | Philosophy, the horizontal-slicing anti-pattern, the four-stage workflow, and the per-cycle checklist |
-| `tests.md` | Skill-root document, cited from Philosophy: worked good and bad test examples |
-| `mocking.md` | Skill-root document, cited from Philosophy: mock at system boundaries only, and what not to mock |
-| `deep-modules.md` | Skill-root document, cited from stage 1: what a deep module is (small interface, large implementation) and why it is the design to aim for |
-| `interface-design.md` | Skill-root document, cited from stage 1: designing interfaces for testability, starting with accepting dependencies rather than creating them |
-| `refactoring.md` | Skill-root document, cited from stage 4: the refactor-candidate checklist — duplication, long methods, shallow modules, feature envy, primitive obsession |
+| `references/tests.md` | Cited from Philosophy: worked good and bad test examples |
+| `references/mocking.md` | Cited from Philosophy: mock at system boundaries only, and what not to mock |
+| `references/deep-modules.md` | Cited from stage 1: what a deep module is (small interface, large implementation) and why it is the design to aim for |
+| `references/interface-design.md` | Cited from stage 1: designing interfaces for testability, starting with accepting dependencies rather than creating them |
+| `references/refactoring.md` | Cited from stage 4: the refactor-candidate checklist — duplication, long methods, shallow modules, feature envy, primitive obsession |

plugins/bin/.apm/skills/tdd/SKILL.md

@@ -18,7 +18,7 @@ metadata:
 
 **Bad tests** are coupled to implementation. They mock internal collaborators, test private methods, or verify through external means (like querying a database directly instead of using the interface). The warning sign: your test breaks when you refactor, but behavior hasn't changed. If you rename an internal function and tests fail, those tests were testing implementation, not behavior.
 
-If you need worked examples of the difference — a behaviour-level test beside the implementation-coupled version of the same check — read `tests.md`. If a test needs a collaborator faked, read `mocking.md` before reaching for a mock.
+If you need worked examples of the difference — a behaviour-level test beside the implementation-coupled version of the same check — read `references/tests.md`. If a test needs a collaborator faked, read `references/mocking.md` before reaching for a mock.
 
 ## Anti-Pattern: Horizontal Slices
 
@@ -55,8 +55,8 @@ Before writing any code:
 
 - [ ] Confirm with user what interface changes are needed
 - [ ] Confirm with user which behaviors to test (prioritize)
-- [ ] Identify opportunities for [deep modules](deep-modules.md) (small interface, deep implementation)
-- [ ] Design interfaces for [testability](interface-design.md)
+- [ ] Identify opportunities for [deep modules](references/deep-modules.md) (small interface, deep implementation)
+- [ ] Design interfaces for [testability](references/interface-design.md)
 - [ ] List the behaviors to test (not implementation steps)
 - [ ] Get user approval on the plan
 
@@ -93,7 +93,7 @@ Rules:
 
 ### 4. Refactor
 
-After all tests pass, look for [refactor candidates](refactoring.md):
+After all tests pass, look for [refactor candidates](references/refactoring.md):
 
 - [ ] Extract duplication
 - [ ] Deepen modules (move complexity behind simple interfaces)