feat(ultraplan-local): v2.3.1 — qualified slug convention for cc-architect-catalog

Resolves v2.3.0 dogfood collision: skill-factory produced a
specialized hooks-pattern.md draft that would have overwritten the
generic seed. Qualified slugs let one feature host multiple named
patterns at different abstraction levels.

Slug convention: <cc_feature>[-<qualifier>]-<layer>.md. Unqualified =
canonical baseline. Qualified = sub-pattern (e.g., hooks-observability-
pattern.md) that does not displace the baseline.

Changes:
- SKILL.md: slug convention section, coverage-table qualified column,
  matcher logic for N patterns per feature, modification rules cover
  qualified-vs-canonical choice and collision handling.
- feature-matcher: catalog map is cc_feature -> {layer -> [skills]};
  selection rules (baseline by default, qualified when justified,
  multi-skill when non-overlapping); supporting_skill accepts list.
- gap-identifier: adds pattern_count[cc_feature] to coverage audit.
- architecture-critic: supporting-skill verification — every cited
  skill name must exist in the catalog (blocker severity).
- First qualified skill: hooks-observability-pattern.md (promoted from
  .drafts/, source ai-psychosis/README.md, ngram-overlap 0.01).
- Version bump 2.3.0 -> 2.3.1 across plugin.json, badges, table, root
  CLAUDE.md, CHANGELOG.

Non-breaking: existing unqualified slugs keep working, no cc_feature
taxonomy changes, hallucination gate unchanged.

plugins/ultraplan-local/agents/architecture-critic.md

@@ -66,6 +66,14 @@ the catalog or fallback list.
 catalog, this is a **major** finding (REVISE — the feature is real but
 the catalog has a coverage gap worth surfacing), not a blocker.
 
+**Supporting-skill verification:** `supporting_skill` entries (one or
+more skill names per feature, following the
+`<feature>[-<qualifier>]-<layer>.md` convention) must match real files
+in the catalog. A cited skill that does not exist is a **blocker**.
+Multiple supporting skills for one feature are allowed when they cover
+non-overlapping aspects — but the `integration_note` must justify
+having more than one.
+
 ### 3. Contradiction detection
 
 Scan for internal contradictions: