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>

packages/brain/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "dist"
+  },
+  "include": ["src"]
+}