feat: Intelligent Skill Dispatch — change-triggered skill selection

[chadjw]

Summary

• Extends the existing 3-layer recommendation engine with 16 new signal types (4 change-type + 12 domain signals) for change-aware skill scoring
• New dispatch_skills MCP tool that auto-detects changes from git diff and recommends an annotated skill sequence with parallel-safe flags, estimated impact, and dependency info
• Session-start integration via HEAD delta detection — automatically recommends skills when the codebase has changed since the last session
• Tiered caching: cached health snapshot by default, --fresh flag to force recapture

19 commits, 168 new tests, all passing. Backward compatible — 44 existing recommendation engine tests unchanged.

New files

• packages/cli/src/skill/dispatch-types.ts — DispatchContext, DispatchResult, DispatchedSkill types
• packages/cli/src/skill/dispatch-engine.ts — Core dispatch engine with signal enrichment, annotation, and git helpers
• packages/cli/src/skill/dispatch-session.ts — Session-start HEAD delta detection and advisory banner
• packages/cli/src/mcp/tools/dispatch-skills.ts — MCP tool adapter

Modified files

• packages/cli/src/skill/recommendation-types.ts — HEALTH_SIGNALS extended from 12 to 28
• packages/cli/src/skill/recommendation-rules.ts — Fallback rules for 15 bundled skills with change/domain addresses
• packages/cli/src/skill/stack-profile.ts — New detectDomainsFromFiles() function
• packages/cli/src/mcp/server.ts — dispatch_skills tool registration
• packages/cli/src/commands/setup-mcp.ts — ALL_MCP_TOOLS updated

Test plan

• 168 new tests pass across 7 test files (types, engine, session, MCP tool, rules, signals)
• 44 existing recommendation engine tests pass unchanged (backward compat)
• TypeScript compiles cleanly with --noEmit
• harness validate passes
• MCP tool registration tests updated for 54 tools (was 53)