feat: @mosaic/coord — migrate from v0, gateway integration (P2-005)

Migrate the orchestration coordination package from v0 with full
file-based mission/task lifecycle management. Adds gateway REST API
at /api/coord/* and agent tools for coord queries.

Package modules:
- types: Mission, task, session, milestone type definitions
- mission: Create, load, save missions with atomic file writes
- tasks-file: TASKS.md markdown table parsing/generation with file locking
- runner: Task execution subprocess spawning with session locks
- status: Mission and task status queries

Gateway integration:
- CoordModule with CoordService wrapping coord functions
- CoordController exposing status/tasks/task-detail endpoints
- Agent tools: coord_mission_status, coord_list_tasks, coord_task_detail

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

pnpm-lock.yaml

@@ -53,6 +53,9 @@ importers:
       '@mosaic/brain':
         specifier: workspace:^
         version: link:../../packages/brain
+      '@mosaic/coord':
+        specifier: workspace:^
+        version: link:../../packages/coord
       '@mosaic/db':
         specifier: workspace:^
         version: link:../../packages/db
@@ -255,6 +258,9 @@ importers:
         specifier: workspace:*
         version: link:../types
     devDependencies:
+      '@types/node':
+        specifier: ^22.0.0
+        version: 22.19.15
       typescript:
         specifier: ^5.8.0
         version: 5.9.3