test(fix-cli): close missed HOME-leak — isolate spawns + lock SKL/COL out

Devil's advocate gap-verification (read-only Workflow, 9 skeptics) refuted the
blanket "all closed" claim by finding fix-cli.test.mjs was the one CLI-spawning
test still reading the real ~/.claude. fix-cli runs the SKL skill-listing
scanner (HOME-scoped) even with includeGlobal:false, so its manual findings
include CA-SKL-001 on a dev machine but not in clean CI.

This directly corrects 325182d, which listed fix-cli.test.mjs as "Proven safe,
left as-is (output byte-identical real vs empty HOME — fixable findings are
project-local HKV/RUL/SET, never SKL/COL)". That reasoning predated SKL being
wired into scan-orchestrator (7bb2547/66433fe) and was false: real HOME yields
manual=6 (incl. CA-SKL-001), hermetic manual=5 (5230 vs 4798 bytes).

- wrap all 5 fix-cli spawns in hermeticEnv() (matches the other 11 CLI tests)
- add a regression lock: a project-scoped run must surface no CA-SKL/CA-COL
- redirect the --apply backup check to HERMETIC_HOME — the test was also
  writing backups into the real ~/.config-audit/backups on every run
- docs: stale "26 hook events" -> 28 (README:528, scanner-internals:73);
  hook-validator.mjs comment April -> June 2026 (functional count already 28)

Re-audited all 12 CLI-spawning test files: 11 hermetic-helper, manifest custom
HOME-env, post-edit-verify safe-by-construction (early-exit only, never reaches
scanners). HOME-leak class now actually closed. Suite 875/875, no snapshot drift.

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

scanners/hook-validator.mjs

@@ -13,7 +13,7 @@ import { resolve, dirname } from 'node:path';
 
 const SCANNER = 'HKV';
 
-/** All valid hook events (as of April 2026) */
+/** All valid hook events (as of June 2026) */
 const VALID_EVENTS = new Set([
   'SessionStart', 'InstructionsLoaded', 'UserPromptSubmit',
   'PreToolUse', 'PermissionRequest', 'PermissionDenied',