chore: drop the flat content mirror and native install support (ADR-0024)

apm becomes the only supported install path. The flat mirror at each plugin
root existed solely so Claude Code's native `claude plugin install` could
convention-scan plugin content (ADR-0017). With no native consumers, it cost
~20,000 tracked lines plus ~2,100 lines of sync tooling and ~88s of every
push to guard content apm never reads — and its only automated gate,
`claude plugin validate --strict`, passes on a plugin with zero content, so
it could not detect the defect ADR-0017 was created to fix.

Removes the mirror (213 files), the six per-plugin manifest pairs,
sync-plugin-content.sh, its 1,289-line test, the orphaned
marketplace-plugins.sh, and the check-plugin-content-sync and
validate-plugins pre-push hooks. The root `marketplace:` block and
.claude-plugin/ catalogue stay: apm's own marketplace consumers read that
same file, so `<name>@holocron` short names keep working.

tests/run-bats.sh now excludes .claude/skills/. apm installs from .apm/,
which carries the tests/ dirs the mirror stripped, so deployed .bats files
would otherwise be discovered and double-run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YR2CjVumUbEGWcMikcoXBD

.pre-commit-config.yaml

@@ -32,11 +32,14 @@ repos:
         # root-anchored and spells that path out. This was five `(^|/)`
         # any-depth alternatives plus one `^` root-only one -- a mixture with no
         # rationale, under which a fixture or vendored tree containing
-        # `.../.claude-plugin/plugin.json` would have been silently excluded from
-        # formatting while an equivalent `.../.agents/plugins/marketplace.json`
-        # would not. All fifteen real files (3 root marketplace manifests, 2 per
-        # plugin x 6 plugins) match; anything else is hand-authored and gets
-        # formatted.
+        # `.../.claude-plugin/marketplace.json` would have been silently excluded
+        # from formatting while an equivalent
+        # `.../.agents/plugins/marketplace.json` would not. The three root
+        # marketplace manifests match; anything else is hand-authored and gets
+        # formatted. The twelve per-plugin `plugin.json` alternatives were
+        # dropped with the plugin manifests themselves when native
+        # `claude plugin install` support was removed -- apm probes `apm.yml`
+        # and never reached them.
         #
         # `.claude/settings.json` is the sixteenth, and it is excluded for a
         # different reason: apm OWNS that file (ADR-0018, ADR-0019), and
@@ -50,7 +53,7 @@ repos:
         # happened when the SessionStart hook first landed in 2e395a4.
         # Re-running `apm install` fixes the file; leaving it in scope here
         # would re-break it on the very commit that carries the fix.
-        exclude: '^(\.claude-plugin/marketplace\.json|\.agents/plugins/marketplace\.json|\.github/plugin/marketplace\.json|plugins/[^/]+/\.claude-plugin/plugin\.json|plugins/[^/]+/\.github/plugin/plugin\.json|\.claude/settings\.json)$'
+        exclude: '^(\.claude-plugin/marketplace\.json|\.agents/plugins/marketplace\.json|\.github/plugin/marketplace\.json|\.claude/settings\.json)$'
       - id: check-yaml
         stages: ['pre-commit']
       - id: trailing-whitespace
@@ -75,15 +78,6 @@ repos:
         pass_filenames: false
         always_run: true
 
-      - id: check-plugin-content-sync
-        name: Check plugin content sync
-        description: Verify each plugin's flat skills/agents/commands/hooks/hooks.json mirror is in sync with .apm/ -- Claude Code has no .apm/ awareness so this compiled mirror must stay current (see issue #90)
-        entry: bash scripts/sync-plugin-content.sh --check --all
-        language: system
-        stages: [pre-push]
-        pass_filenames: false
-        always_run: true
-
       - id: check-executables-allow-sync
         name: Check executables allow key sync
         description: Verify root apm.yml's executables.allow key names kyberforge's actual version -- apm matches that key by exact "<package>#<version>" lookup, so a version bump on one side alone silently stops deploying kyberforge's hooks/ and bin/ and lets the apm install go stale (see ADR-0019)
@@ -202,15 +196,6 @@ repos:
         pass_filenames: false
         always_run: true
 
-      - id: validate-plugins
-        name: Validate plugins
-        description: Run claude plugin validate --strict on every plugin directory
-        entry: bash -c 'for d in plugins/*/; do claude plugin validate --strict "$d" || exit 1; done'
-        language: system
-        stages: [pre-push]
-        pass_filenames: false
-        always_run: true
-
       - id: validate-marketplace
         name: Validate marketplace manifest
         description: Run claude plugin validate --strict on the root marketplace manifest