fix: gen-skill-docs resolver merge + preamble tier gate + plan file discovery

The local RESOLVERS record in gen-skill-docs.ts was shadowing the imported
canonical resolvers, causing stale test coverage and preamble generators
to be used instead of the authoritative versions in resolvers/.

Changes:
- Merge imported RESOLVERS with local overrides (spread + override pattern)
- Fix preamble tier gate: tier 1 skills no longer get AskUserQuestion format
- Make plan file discovery host-agnostic (search multiple plan dirs)
- Add missing E2E tier entries for ship/review plan completion tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/helpers/touchfiles.ts

@@ -184,6 +184,7 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'review-base-branch': 'gate',
   'review-design-lite': 'periodic',   // 4/7 threshold is subjective
   'review-coverage-audit': 'gate',
+  'review-plan-completion': 'gate',
 
   // Office Hours
   'office-hours-spec-review': 'gate',
@@ -208,6 +209,8 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'ship-local-workflow': 'gate',
   'ship-coverage-audit': 'gate',
   'ship-triage': 'gate',
+  'ship-plan-completion': 'gate',
+  'ship-plan-verification': 'gate',
 
   // Retro — gate for cheap branch detection, periodic for full Opus retro
   'retro': 'periodic',