feat(scripts): add evaluate-library skill + supporting files

Adds the /evaluate-library skill runbook at .claude/skills/evaluate-library/
with SKILL.md (8-filter + 3-prompt protocol, collect-cheap-skip-expensive
ordering, trace-write step, skip sentinel), POLICY.md (ADR-022 summary
≤2 pages), TRACE-TEMPLATE.md (complete YAML frontmatter + 11 headings in
order), and EXAMPLES/ with one approved (clsx) and one rejected
(trpc-to-openapi, named-consumer: fail) worked trace.

Updates session-start.sh to surface the skill in session pointers.
The skill is auto-registered by the harness on SKILL.md creation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/hooks/session-start.sh

@@ -11,7 +11,7 @@ Generator-first: pnpm turbo gen <kind> beats hand-rolled scaffolding (non-negoti
 Conformance: pnpm conformance + pnpm fallow (5-gate drift detection)
 Conventional Commits (non-negotiable): <type>(<scope>): <subject> — see CLAUDE.md Key Conventions
 Releases: release-please reads commits + opens rolling release PR on merge to main (ADR-021)
-Skills: to-prd, grill-with-docs, grill-me, handoff, improve-codebase-architecture (.claude/skills/)
+Skills: to-prd, grill-with-docs, grill-me, handoff, improve-codebase-architecture, evaluate-library (.claude/skills/)
 EOF
 
 exit 0