feat(skill-listing): add SKL scanner for the skill-listing token budget

Fase 4 Items 2+3 (CC 2.1.114→181 gap-review). New orchestrated scanner
`skill-listing-scanner.mjs` (prefix SKL) flags every active skill whose
description exceeds the verified 1,536-char listing cap (CC 2.1.105, changelog
L1502). Past the cap, Claude Code silently truncates the description the model
reads to route skill invocation — dropping the trigger phrases at the tail.
HOME-scoped over all user + plugin skills via enumerateSkills (COL is the model).

- CA-SKL-001 (medium): description > 1,536 chars. Remediation folds in Item
  2(b) — recommends disableBundledSkills + skillOverrides + trimming
  (designvalg A: no standalone GAP-check, which would fire for nearly everyone).
- Designvalg B: v1 ships the verified cap ONLY. The aggregate 2%-of-context
  listing budget is deferred — it needs a context-window assumption that would
  turn a verified fact into a guess (would carry a CALIBRATION_NOTE if added).
- Choice C: recognize the skillOverrides settings key (CC 2.1.129) in
  KNOWN_KEYS. Left OUT of TYPE_CHECKS — the value is a per-skill object
  (off/user-invocable-only/name-only), not a string; a 'string' check (as the
  plan sketched) would create a NEW false positive. Verify-first deviation.

Registration: scan-orchestrator (13th scanner), humanizer (SKL → 'Wasted
tokens' + static/_default translations), scoring SCANNER_AREA_MAP (→ Token
Efficiency; no 11th area), README badge 12→13, CLAUDE.md (finding-id +
test-count), docs/scanner-internals.md, gap-matrix + plan status notes.

Snapshots reseeded hermetically (SEED_SNAPSHOT/UPDATE_SNAPSHOT): SKL entry with
0 findings in empty HOME, scanners_ok 11→12, claudeMdEstimatedTokens bump from
the CLAUDE.md edits flowing through the cascade. Contamination grep clean.

Suite 868/868 (856 baseline + 11 SKL + 1 skillOverrides). RED→GREEN logged
per cycle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8

tests/scanners/settings-validator.test.mjs

@@ -131,7 +131,7 @@ describe('SET scanner — CC 2.1.114→181 valid keys (Batch 1 false-positive fi
     'sandbox', 'fallbackModel', 'enforceAvailableModels', 'disableBundledSkills',
     'pluginSuggestionMarketplaces', 'requiredMinimumVersion', 'requiredMaximumVersion',
     'allowAllClaudeAiMcps', 'footerLinksRegexes', 'wheelScrollAccelerationEnabled',
-    'parentSettingsBehavior',
+    'parentSettingsBehavior', 'skillOverrides',
   ];
 
   beforeEach(async () => {
@@ -152,6 +152,7 @@ describe('SET scanner — CC 2.1.114→181 valid keys (Batch 1 false-positive fi
       footerLinksRegexes: ['^https://internal\\.'],              // CC 2.1.181
       wheelScrollAccelerationEnabled: true,                      // CC 2.1.174
       parentSettingsBehavior: 'merge',                           // CC 2.1.133
+      skillOverrides: { 'example-skill': 'name-only' },          // CC 2.1.129 (per-skill object)
       permissions: { deny: ['Read(./.env)'], allow: ['Bash(npm run *)'] },
     };
     await writeFile(