feat(cli): command architecture — agents, missions, and gateway-aware prdy

DB schema:
- Extend agents table with projectId, ownerId, systemPrompt, allowedTools,
  skills, isSystem columns and indexes
- Add agentId FK to conversations table with index

Brain:
- New agents repository (findAll, findById, findByName, findByProject,
  findSystem, findAccessible, create, update, remove)
- Wire into Brain interface and createBrain factory

Gateway:
- New AgentConfigsController at /api/agents with full CRUD + ownership guards
- Consolidate /api/missions — user-scoped CRUD replaces old project-ownership
  model, add /api/missions/:id/tasks sub-routes (replaces coord mission-tasks)
- Slim coord controller to file-based endpoints only (agent tool consumption)
- Remove DB-backed methods from CoordService (now handled by Brain repos)
- Wire agentConfigId into AgentService.createSession for DB config merging
- Add agentId field to ChatSocketMessageDto and ChatMessagePayload

CLI:
- New `mosaic agent` command (--list, --new, --show, --update, --delete)
- New `mosaic mission` command (--list, --init, --plan, --update, task sub)
- New `mosaic prdy` gateway-aware wrapper (--init, --update, --project)
- Shared with-auth helper and select-dialog utility
- TUI: accept --agent and --project flags, pass agentId to socket, display
  agent name in top bar
- Gateway API client: add agents, projects, missions, mission-tasks helpers
- Add @clack/prompts dependency
- Refactor sessions commands to use with-auth helper

Types:
- Add agentId to ChatMessagePayload

Tests:
- Update resource-ownership test for user-scoped missions (NotFoundException)

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

pnpm-lock.yaml

@@ -286,6 +286,9 @@ importers:
 
   packages/cli:
     dependencies:
+      '@clack/prompts':
+        specifier: ^0.9.0
+        version: 0.9.1
       '@mosaic/mosaic':
         specifier: workspace:^
         version: link:../mosaic