feat(skills): ship ue-design-skills bundle, licensing and delivery gate

Phase 0 of the handoff plan, as a marketplace rather than a flat skills/
directory. Content moved out of the LyraResearch archive and depersonalised:
addresses stay in the archive, recipes ship.

- plugins/ue-design-skills: 17 skills, 232 failure-mode entries, each with the
  six required fields; catalog.json as the harness-neutral source of truth and
  .claude-plugin/ as one adapter over it.
- _gate: 16 rules, one poisoned fixture per rule, plus surface coverage so a
  declared file cannot silently miss the line rules.
- ADR-0002 (harness-neutral bundle behind a marketplace) and ADR-0003 (split
  licensing: CC BY-ND 4.0 prose, Apache-2.0 code and metadata).
- LICENSE files at both levels, CONTRIBUTING.md, docs/licensing-options.md as
  the material the licence decision grew from.

Verified: gate.py 0 violations; test_gate.py 16/16 rules redden on their
fixtures with a clean baseline and 2 root files reaching the line rules.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

plugins/ue-design-skills/.claude-plugin/plugin.json

@@ -0,0 +1,16 @@
+{
+  "name": "ue-design-skills",
+  "version": "0.1.0",
+  "description": "Design-review skills for Unreal Engine 5.6 projects: modular gameplay, GAS, input, UI, messaging, tags, network authority, cosmetics, settings, asset loading, streaming budgets, allocation. Norms plus reproducible failure-mode detection recipes.",
+  "author": {
+    "name": "MagentaDolphin"
+  },
+  "license": "CC-BY-ND-4.0",
+  "keywords": [
+    "unreal-engine",
+    "ue5",
+    "gameplay-ability-system",
+    "game-features",
+    "architecture-review"
+  ]
+}