feat(tokens): stale plugin-cache disk-cleanup finding, honestly labelled Dead config (v5.9 B3b)

The B3a cache filter already exposes discovery.staleCacheVersions; surface them
as a finding so the user knows the superseded plugin versions are safe to delete.

Honesty (Verifiseringsplikt): the finding loads on ZERO turns, so it must NOT
read as a per-turn token cost. TOK normally humanizes to "Wasted tokens"; a new
per-finding category override ('plugin-cache-hygiene' -> "Dead config") plus a
dedicated humanizer translation ("Old plugin versions are sitting on disk (safe
to delete) ... cost zero tokens per turn ... housekeeping, not a performance
problem") keep the prose accurate instead of the generic "using more space"
default. evidence carries the explicit "zero live-context impact" note.

- token-hotspots: Pattern H emits CA-TOK (low) from discovery.staleCacheVersions
  when stale versions exist (`--global`); silent otherwise.
- humanizer: CATEGORY_TO_IMPACT lets a finding's category override the
  scanner-default impact label (raw `category` field unchanged -> --json/--raw
  byte-stable). humanizer-data: honest static translation for the finding.
- Tests: finding fires/severity/category, lists stale keys + zero-impact note,
  silent when none; humanizer override -> Dead config; honest translation locked.
- Docs: tokens command render note (disk-cleanup, not a token problem) +
  --no-exclude-cache flag; README + CLAUDE.md rows (7 patterns, cache-aware).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scanners/lib/humanizer-data.mjs

@@ -569,6 +569,11 @@ export const TRANSLATIONS = {
         description: 'Skill descriptions load on every turn whether you use the skill or not. Long descriptions add up.',
         recommendation: 'Trim the description to one short sentence and move details into the skill body.',
       },
+      'Stale plugin-cache versions (disk cleanup, zero live-context impact)': {
+        title: 'Old plugin versions are sitting on disk (safe to delete)',
+        description: 'Your plugin cache holds older versions that newer installs have replaced. They take up disk space but are never loaded into a conversation — so they cost zero tokens per turn. This is housekeeping, not a performance problem.',
+        recommendation: 'Delete the old version folders to reclaim disk. The details list exactly which ones; the active version of each plugin stays untouched.',
+      },
     },
     patterns: [
       {