feat(5.21): Tasks Plugin — activities with status, priority, due dates, ARQ reminders

- New builtin plugin app/plugins/builtins/tasks/ with full CRUD
- Task model with TenantMixin (title, description, status, priority, due_date, assigned_to, contact_id)
- Routes: GET/POST /tasks, GET/PATCH/DELETE /tasks/{id}, POST /tasks/{id}/assign, POST /tasks/{id}/status
- All routes RBAC-protected (tasks:read, tasks:write, tasks:delete)
- ARQ cron job tasks_due_reminder (daily 8:00) sends notifications for due tasks
- Migration 0001_initial.sql creates tasks table with indexes
- Frontend: Tasks.tsx page with list, filter, create/edit modal, detail modal
- Frontend: api/tasks.ts with React Query hooks
- Route /tasks in routes/index.tsx, sidebar entry via plugin manifest
- i18n keys for nav.tasks and tasks.* in de.json and en.json
- Tests: test_tasks.py (11 tests) + Tasks.test.tsx (3 tests)
- Registered TasksPlugin in conftest.py and worker.py

app/core/worker.py

@@ -53,6 +53,7 @@ from app.plugins.builtins.automation.scheduler import scheduler_tick
 from app.plugins.builtins.automation.workflow_timeout import check_workflow_timeouts
 from app.plugins.builtins.automation.agent_runner import run_agent
 from app.plugins.builtins.automation.execution_engine import run_automation
+from app.plugins.builtins.tasks.jobs import tasks_due_reminder
 
 
 class WorkerSettings:
@@ -69,6 +70,7 @@ class WorkerSettings:
         check_workflow_timeouts,
         run_agent,
         run_automation,
+        tasks_due_reminder,
     ]
     redis_settings = _get_redis_settings()
     on_startup = on_startup
@@ -79,4 +81,5 @@ class WorkerSettings:
     cron_jobs = [
         cron(scheduler_tick, second={0, 30}),
         cron(check_workflow_timeouts, minute={0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55}),
+        cron(tasks_due_reminder, hour=8, minute=0),
     ]