fix(kyberforge): bridge apm content to Claude Code's flat plugin discovery

Claude Code's (and Copilot's) native plugin installer has zero awareness of
.apm/ nesting -- it convention-scans only flat skills/, agents/, commands/,
hooks.json at each plugin's root. Confirmed via strings on the installed
claude binary and live installs of git@holocron/gitea@holocron/kyberforge@
holocron, all reporting Skills(0) Agents(0) Hooks(0) post ADR-0015's apm
conversion. Root cause (apm_cli/core/plugin_manifest.py): apm's plugin.json
compiler deliberately strips skills/agents/commands keys, assuming the host
already auto-discovers those convention directories -- it has no model of
.apm/ being host-visible at all. Separately, apm's own bundle exporter
(apm_cli/bundle/plugin_exporter.py, behind `apm pack --format plugin`)
implements the correct .apm/ -> flat mapping, but only ever targeted
build/<name>-<version>/, a path nothing in marketplace.json's source: points
at.

scripts/sync-plugin-content.sh wraps that bundle exporter and copies its
agents/, skills/, commands/, instructions/, extensions/, and merged
hooks.json back into each plugin's own root as a second tracked
compiled-output category -- same governance status as
.claude-plugin/plugin.json: generated from .apm/, never hand-edited. tests/
subdirectories are excluded from the mirror (dev fixtures, not host-visible
runtime content; several hardcode a relative repo-root walk-up sized for the
.apm/-nested depth, which breaks when duplicated one level shallower).
Applied for real across all 6 plugins and verified two ways: `claude plugin
validate --strict` passes on every real plugin directory, and a live
`claude --plugin-dir <path> -p "list skills/agents"` behavioral test
confirms content is now actually discovered.

Also, from the same issue #90 review round:
- scripts/check-manifests.sh pointed at each plugin's root-level plugin.json
  (checking skills/hooks/mcpServers/agents pointer fields) -- that file was a
  stale near-duplicate of .claude-plugin/plugin.json nothing else read or
  wrote, now deleted across all 6 plugins. check-manifests.sh is rewritten to
  validate .claude-plugin/plugin.json instead, and drops the pointer-field
  checks entirely (nothing to check -- those fields are correctly absent by
  design). Content-presence drift is now check-plugin-content-sync's job, a
  new pre-push hook wired in .pre-commit-config.yaml.

docs/adr/0017 records the root cause and decision in full, including two
rejected alternatives (patching plugin.json's path fields directly -- apm's
compiler strips them on every run; pointing marketplace.json at apm pack's
build/ output -- a version-suffixed non-source directory nothing can install
from without an extra build step). ADR-0015 and CONTEXT.md are updated to
point at it.

Refs: #90

plugins/kyberforge/skills/skill-author/assets/templates/SKILL.md

@@ -0,0 +1,105 @@
+---
+# SKILL.md — agentskills.io skill definition
+# Fill in all FILL IN: placeholders. Remove comment blocks that don't apply.
+
+name: SKILL_NAME
+# Required. Must exactly match the parent directory name.
+# Valid characters: lowercase letters, numbers, hyphens.
+# Invalid: uppercase, leading/trailing/consecutive hyphens.
+# Max length: 64 characters.
+# Examples: my-tool, data-analyzer, pdf-processor
+
+description: >
+  FILL IN: What does this skill do? State capabilities specifically
+  (e.g. "parses and validates OpenAPI specs", not "helps with APIs").
+  Use when FILL IN: when should an agent activate this skill?
+  Include indirect triggers: even if the user doesn't mention X explicitly.
+  Do not use when FILL IN: near-miss exclusions — remove this line if none apply.
+
+# license: MIT
+# Optional. License name (e.g. MIT, Apache-2.0) or relative path to a bundled
+# license file. Include when distributing this skill. Omit for private/internal use.
+
+# compatibility: Requires python3 >= 3.10 and uv
+# Optional. 1–500 characters. State tool requirements, runtime versions,
+# and network access needs. Omit for skills with no special environment requirements.
+
+# metadata:
+#   author: your-name
+#   version: "1.0"
+#   category: general
+#   source_keys:
+#     - source-slug-one
+#     - source-slug-two
+# Optional. Arbitrary key-value map. Common keys: author, version, category.
+# source_keys: populated when built from /research output. Lists slugs from references/sources.md.
+# Also add source_keys to each references/*.md file that was informed by research.
+
+# allowed-tools: Bash Read Write
+# Optional (experimental — support varies by client).
+# Space-separated list of pre-approved tools.
+# Use when tool usage is known and bounded, to reduce permission prompts.
+---
+
+<!-- ============================================================
+  SKILL BODY
+
+  Include only what the agent lacks:
+    - Domain conventions the agent cannot infer from general knowledge
+    - Non-obvious sequences or ordering constraints
+    - One default per decision point + one escape hatch (never a menu)
+    - Gotchas — facts that defy reasonable assumptions
+
+  Omit:
+    - Concepts the agent already knows
+    - Exhaustive option lists
+    - Steps the agent handles independently
+    - Restatements of the description
+
+  Size budget: under 500 lines / 5000 tokens.
+  Move reference material to references/ and load it conditionally.
+  Bundle repeated executable logic into scripts/.
+
+  Delete this comment block before shipping.
+============================================================ -->
+
+<!-- OPTIONAL: Gotchas section — highest-value content. Place near the top.
+     Add facts that defy reasonable assumptions or non-obvious constraints.
+
+## Gotchas
+
+- FILL IN: fact that defies a reasonable assumption
+- FILL IN: non-obvious naming discrepancy or hidden constraint
+-->
+
+<!-- OPTIONAL: Multi-step workflow checklist.
+
+## Workflow
+
+- [ ] Step 1: FILL IN
+- [ ] Step 2: FILL IN
+- [ ] Step 3: FILL IN
+-->
+
+<!-- OPTIONAL: Output format template — use when the agent must produce a specific format.
+
+## Output format
+
+Use this structure:
+
+```markdown
+# [FILL IN: Title]
+
+## FILL IN: Section
+FILL IN: what goes here
+```
+-->
+
+<!-- OPTIONAL: Conditional reference — load documentation only when needed.
+
+If FILL IN: condition, read `references/FILL IN: filename.md`.
+-->
+
+## FILL IN: <section-name (e.g. Step 1, Workflow, Instructions)>
+
+FILL IN: Add your skill instructions here. Replace this section header and body with your skill content.