fix: Comprehensive validation and bug fixes

Infrastructure:
- Add Redis and Celery workers to all docker-compose files
- Fix celery migration race condition in entrypoint.sh
- Add healthchecks and resource limits to dev compose
- Update .env.template with Redis/Celery variables

Backend Models & Schemas:
- Rename Sprint.completed_points to velocity (per requirements)
- Add AgentInstance.name as required field
- Rename Issue external tracker fields for consistency
- Add IssueSource and TrackerType enums
- Add Project.default_tracker_type field

Backend Fixes:
- Add Celery retry configuration with exponential backoff
- Remove unused sequence counter from EventBus
- Add mypy overrides for test dependencies
- Fix test file using wrong schema (UserUpdate -> dict)

Frontend Fixes:
- Fix memory leak in useProjectEvents (proper cleanup)
- Fix race condition with stale closure in reconnection
- Sync TokenWithUser type with regenerated API client
- Fix expires_in null handling in useAuth
- Clean up unused imports in prototype pages
- Add ESLint relaxed rules for prototype files

CI/CD:
- Add E2E testing stage with Testcontainers
- Add security scanning with Trivy and pip-audit
- Add dependency caching for faster builds

Tests:
- Update all tests to use renamed fields (velocity, name, etc.)
- Fix 14 schema test failures
- All 1500 tests pass with 91% coverage

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/celery_app.py

@@ -64,6 +64,12 @@ celery_app.conf.update(
     result_expires=86400,
     # Broker connection retry
     broker_connection_retry_on_startup=True,
+    # Retry configuration per ADR-003 (built-in retry with backoff)
+    task_autoretry_for=(Exception,),  # Retry on all exceptions
+    task_retry_kwargs={"max_retries": 3, "countdown": 5},  # Initial 5s delay
+    task_retry_backoff=True,  # Enable exponential backoff
+    task_retry_backoff_max=600,  # Max 10 minutes between retries
+    task_retry_jitter=True,  # Add jitter to prevent thundering herd
     # Beat schedule for periodic tasks
     beat_schedule={
         # Cost aggregation every hour per ADR-012