feat(skill-listing): add CA-SKL-002 aggregate listing-budget check

Syklus 2 of Fase 4 Items 2+3. Flags when the sum of active skill
descriptions exceeds the listing budget (~2% of context, CC 2.1.32).

Design (operator-confirmed "fact-first, 200k anchor"):
- low severity (estimate) vs medium for the verified 1,536-char cap
- each description counted up to the 1,536 cap (what actually loads in
  the listing) — avoids double-counting the tail CA-SKL-001 flags
- fires when sum > 2% x 200k = 4000 tok; evidence leads with the measured
  sum + a calibration note that the budget scales 5x on 1M-context models
- aggregate emitted after the per-skill loop so the common case reads
  001=cap, 002=aggregate (finding IDs are a sequential counter, not stable
  semantic IDs — tests match on title, never NNN)

Also:
- tailored humanizer static entry for the aggregate title
- fix latent HOME leak in posture-grade-stability.test.mjs: it spawned
  posture.mjs without hermeticEnv(), so a real ~/.claude leaked HOME-scoped
  SKL/COL findings into the baseline grade (Token Efficiency A->B). Now
  isolated like the 8 other CLI-spawning tests.
- docs sync: test count 868->875, scanner-internals, gap-matrix, plan status

Suite 875/875, no snapshot drift, self-audit clean.

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

scanners/lib/humanizer-data.mjs

@@ -742,6 +742,11 @@ export const TRANSLATIONS = {
         description: 'Claude Code only shows the first part of each skill\'s description when it decides which skill to use. This one runs past the limit, so the end — often the trigger phrases — is silently dropped.',
         recommendation: 'Shorten the description so the trigger words come first and it fits under the limit. For skills you do not use, turning them off frees up the listing entirely.',
       },
+      'Aggregate skill descriptions may exceed the listing budget': {
+        title: 'All your skills together may be too much for the listing',
+        description: 'Claude Code keeps every active skill\'s description in one shared listing it reads to choose which skill to use, and that listing has a limited size. Added up, your skills\' descriptions run past that size on a smaller setup, so Claude Code may drop some of them — and stop seeing those skills. This is an estimate; a larger setup has more room.',
+        recommendation: 'Free up room: turn off bundled skills you do not use, collapse the heaviest ones so only their names show, or shorten the longest descriptions. The details show the measured total and the room available.',
+      },
     },
     patterns: [],
     _default: {