feat(alerts): price alerts system (API, evaluator worker, notifications, UI) (M2-EPIC4)

[Shakalito]

Summary

Implements a complete price alerts system covering backend, evaluation logic, notifications, and frontend UI.

Users can create price threshold alerts (ABOVE / BELOW), monitor them via UI, and have them automatically evaluated against live market quotes.

Backend (Alerts API)

• Added price_alerts DB model with full CRUD.
• Endpoints:
  • POST /alerts
  • GET /alerts/me?active=true|false
  • PATCH /alerts/{id} (enable / disable)
  • DELETE /alerts/{id}
• Validates listing existence.
• Uses enum-based alert condition (ABOVE, BELOW).
• Currency is derived server-side from listing metadata (frontend does not provide it).
• Proper ownership checks and timestamp updates.

Alert Evaluator Worker

• Added alert evaluator that:
• polls active alerts,
• fetches batch quotes from Finnhub,
• evaluates alert conditions,
• deactivates triggered alerts and sets last_triggered_at.
• Idempotent on reruns (already-triggered alerts are skipped).
• Currently executed manually via script.

Notifications

• Added minimal notification service:
  • console notifier (active),
  • SMTP notifier scaffold (draft).
• Notification is sent on alert trigger using user’s email.

Frontend (Alerts UI)

• Added alerts pages:
  • /alerts – list, filter (active / inactive / all), enable/disable, delete.
  • /alerts/new – create alert with listing search dropdown.
• Integrated with backend alerts API.
• Currency is display-only and derived from listing.
• Routes integrated into app navigation.

Testing

• Manual verification performed:
• Create / list / toggle / delete alerts via UI and Swagger.
• Alert evaluator correctly triggers and deactivates alerts.
• Invalid listing IDs return 404.
• Invalid currency values rejected by validation.

Notes / Future Improvements (non-blocking)

• Consistency: unify quote batch result keys (UUID vs string) across services.
• Metrics: extend evaluator stats (separate counters for skipped-by-error vs skipped-by-missing-price).
• Execution model:
  • current: manual one-off execution from terminal,
  • future: loop-based worker or dedicated alert-worker service (Docker).
    These are cosmetic / architectural improvements and do not block MVP functionality.

Closes #14 Ref #30, #31, #32, #33

[dazw00110]

All functionalities described in the PR have been manually verified and are working correctly:

• Backend & DB: The price_alerts model stores data correctly, and CRUD operations (create, read, update, delete) work flawlessly via the API.
• Alert Evaluator: The run_alert_evaluator.py script correctly fetches prices from Finnhub and reacts to ABOVE/BELOW conditions. A test on AAPL (target 10 USD) confirmed that alerts are properly triggered and deactivated.
• UI (Frontend): The /alerts page and /alerts/new form are fully integrated with the backend. Filtering and Enable/Disable/Delete buttons work as described.
• Notifications: The system correctly records the alert trigger by saving the last_triggered_at date in the database.

I have noticed that a new Issue has already been created regarding the "Future Improvements" note.