feat(config-audit): cross-plugin collision scanner COL (v5 N6) [skip-docs]

New COL scanner detects skill-name collisions across plugins and
between user-level skills (~/.claude/skills/) and plugin-bundled
skills. Skill identity is the directory basename — matches how
enumerateSkills resolves names.

Detection rules (per docs/v5-namespace-research.md, confidence: medium):
- Plugin-vs-plugin same skill name → severity low (CA-COL-001)
- User-vs-plugin same skill name → severity medium (CA-COL-001)
- Plugin-vs-built-in collisions: out of scope for v5.0.0 (insufficient
  verification — recorded for v5.0.1 follow-up).

Findings carry details.namespaces array with {source, name, path} for
every conflicting source — supports per-collision reporting downstream.

output.mjs: finding() helper now passes through optional `details`
field (scanner-specific structured payload).

scoring.mjs: COL → "Plugin Hygiene" (new area, 10 total). Posture test
updated from 9 → 10 area scores.

.gitignore: docs/v5-namespace-research.md is local-only (Step 22a
research output, gitignored per plan).

Fixture collision-plugins/fake-home/ has user skill `review` colliding
with plugin-a + plugin-b's `review` (medium severity), plus plugin-c's
unique `summarize` (no collision).

[skip-docs] reason: v5 plan fences off README/CLAUDE.md badge updates
to Session 5; Forgejo pre-commit-docs-gate hook requires this tag.

Tests: 617 → 625 (+8).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

plugins/config-audit/scanners/scan-orchestrator.mjs

@@ -26,6 +26,7 @@ import { scan as scanGap } from './feature-gap-scanner.mjs';
 import { scan as scanTokenHotspots } from './token-hotspots.mjs';
 import { scan as scanCachePrefix } from './cache-prefix-scanner.mjs';
 import { scan as scanDisabledInSchema } from './disabled-in-schema-scanner.mjs';
+import { scan as scanCollision } from './collision-scanner.mjs';
 
 // Directory names that identify test fixture / example directories
 const FIXTURE_DIR_NAMES = ['tests', 'examples', '__tests__', 'test-fixtures'];
@@ -59,6 +60,7 @@ const SCANNERS = [
   { name: 'TOK', fn: scanTokenHotspots, label: 'Token Hotspots' },
   { name: 'CPS', fn: scanCachePrefix, label: 'Cache-Prefix Stability' },
   { name: 'DIS', fn: scanDisabledInSchema, label: 'Disabled-In-Schema' },
+  { name: 'COL', fn: scanCollision, label: 'Plugin Skill Collision' },
 ];
 
 /**