feat(brain): @mosaic/brain structured data service (#10)

Implement @mosaic/brain — typed structured data service with MCP + REST API,
JSON file backend, and schema validation via Zod.

Collections: tasks, projects, events, agents, tickets, appreciations,
missions, mission_tasks.

MCP tools: brain_tasks, brain_projects, brain_events, brain_agents,
brain_tickets, brain_today, brain_stale, brain_stats, brain_search,
brain_audit, brain_missions, brain_mission, brain_mission_tasks,
plus mutation tools for all collections.

REST API mirrors MCP 1:1 at /v1/*.
Bearer token auth with timing-safe comparison.
Fastify server with per-request MCP instances (stateless HTTP transport).
JSON file storage with proper-lockfile for concurrent access.

Also adds Brain* types to @mosaic/types.

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

docs/scratchpads/brain-service.md

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+# Scratchpad: @mosaic/brain Structured Data Service
+
+**Issue:** #10
+**Branch:** feat/brain-service
+**PRD:** jarvis-brain/docs/planning/MOSAIC-BRAIN-MEMORY-PRD.md
+
+## Objective
+
+Implement @mosaic/brain as a Fastify service exposing structured data (tasks, projects, events, missions, etc.) via MCP + REST with JSON file backend.
+
+## Plan
+
+1. [x] Add brain data types to @mosaic/types
+2. [ ] Scaffold packages/brain/ with Fastify + MCP SDK
+3. [ ] Implement JSON file storage adapter with locking
+4. [ ] Implement collections: tasks, projects, events, agents, tickets, appreciations, missions, mission_tasks
+5. [ ] Implement MCP tools (query + mutation + mission)
+6. [ ] Implement REST API (mirrors MCP)
+7. [ ] Bearer token auth middleware
+8. [ ] brain_today computed endpoint
+9. [ ] brain_stale, brain_stats, brain_audit, brain_search, brain_graph
+10. [ ] Dockerfile + docker-compose
+11. [ ] Tests
+12. [ ] Code review
+13. [ ] Commit, push, PR, merge
+
+## Progress
+
+- 2026-03-10: Issue #10 created, branch created, starting implementation
+
+## Risks
+
+- Types package already has `Task`/`TaskStatus`/`TaskPriority` for queue — need namespacing
+- Large implementation surface — focus on core CRUD first, computed endpoints second
+
+## Decisions
+
+- Brain types exported from `@mosaic/types` under `Brain` prefix to avoid queue type conflicts
+- JSON storage uses one file per collection
+- In-memory index rebuilt on startup