Extended collaboration: subtasks, claim, assign-group, workload tracking

- 3 new DB tables: subtasks, task_collaboration, user_groups
- Subtasks CRUD with auto-complete parent when all done
- Collaboration requests: assign, transfer, collaborate, claim
- Claim = instant, others need approval (accept/reject)
- Assign to whole user group at once
- Workload tracking: per-user active/completed/pending
- User groups (teams) CRUD with member management
- 39/39 tests passed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/src/index.js

@@ -72,6 +72,7 @@ const start = async () => {
     await app.register(require("./routes/projects"), { prefix: "/api/v1" });
     await app.register(require("./routes/deploy"), { prefix: "/api/v1" });
     await app.register(require("./routes/system"), { prefix: "/api/v1" });
+    await app.register(require("./routes/collaboration"), { prefix: "/api/v1" });
 
     try {
         await app.listen({ port: process.env.PORT || 3000, host: "0.0.0.0" });