feat(install): wire impeccable into the toolchain — deterministic design floor + /impeccable verbs

Complementary to frontend-design (kept: build-time aesthetic direction).
impeccable adds what the chain lacked: 45 deterministic anti-slop rules
(npx impeccable detect, exit 0/2, --json) — the design counterpart of the
semgrep gate — plus 23 design verbs under one /impeccable skill and
persistent per-project design context.

- plugins.lock.json: CLI pinned 3.2.0 (rules update = audit output change
  on unchanged code, LRN-077 class); skill dist = its own release track
- install-plugins.sh Step 8d: staged npx install (tmpdir) -> moved to
  skills-external/impeccable (machine-owned, gitignored, ctx7 pattern);
  never writes through the ~/.claude/skills symlink into the tracked tree
- update-all.sh: pin-honored refresh, Node<24 or failure -> dist kept
- Node >= 24 required (host at 22): steps skip gracefully, activation
  deferred to a deliberate Node bump
- link.sh EXTERNAL_SKILLS, profiles (design/web/web-full/full),
  plugin-advisor, CLAUDE.md design routing, design-gate, README, CHANGELOG
- NOT in design GATE-BLOCK yet: promotion after first dogfood

plugins.lock.json

@@ -37,5 +37,10 @@
     "path": "skills/emil-design-eng/SKILL.md",
     "managed_by": "curl",
     "note": "Emil Kowalski's design engineering skill — UI polish, animations, component craft. Downloaded to skills-external/emil-design-eng/, symlinked by link.sh."
+  },
+  "impeccable": {
+    "source": "npm:impeccable",
+    "version": "3.2.0",
+    "note": "Design anti-pattern detector (45 deterministic rules, CLI 'impeccable detect', exit 0/2) + /impeccable skill (23 verbs) by pbakaus. Pin = CLI version; the skill dist has its own release track fetched by 'skills install'. Pinned for audit reproducibility (LRN-077 class: a rules update silently changes audit output). Requires Node >= 24 — install step skips gracefully below that. Machine-owned: synced to skills-external/impeccable/ (gitignored), symlinked by link.sh."
   }
 }