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/README.md

@@ -0,0 +1,51 @@
+# SKILL_NAME
+
+<!-- FILL IN: One sentence describing what this skill does. -->
+
+## What it does
+
+<!-- FILL IN: 2–4 sentences. What task does this skill handle?
+     What does the agent produce or accomplish when it runs? -->
+
+## Before you start
+
+<!-- FILL IN: List any prerequisites the user should have ready.
+     Examples: research docs, a grill session, specific input files, credentials.
+     Delete this section if the skill has no meaningful prerequisites. -->
+
+## Usage
+
+```
+/SKILL_NAME
+```
+
+<!-- FILL IN: Add any required or common arguments.
+     If the skill takes no arguments, delete the code block above and just keep the slash command. -->
+
+<!-- OPTIONAL: Manual (human) workflow — include if the skill bundles scripts a human can run directly.
+
+**Manual workflow:**
+```bash
+# FILL IN: step-by-step commands
+```
+-->
+
+## Files
+
+<!-- FILL IN: List each file individually. Remove rows for directories you deleted.
+     Replace the example rows below with your actual files. -->
+
+| File | Purpose |
+|------|---------|
+| `SKILL.md` | Skill instructions for agents |
+| `scripts/your-script.sh` | FILL IN: what this script does |
+| `references/your-doc.md` | FILL IN: what this reference covers |
+| `assets/your-asset.json` | FILL IN: what this asset is |
+| `tests/your-test.bats` | FILL IN: what this test covers |
+
+<!-- OPTIONAL: Spec reference — include if this skill implements or follows an external standard.
+
+## Spec reference
+
+[FILL IN: Spec name](FILL IN: URL)
+-->