Feature: Stateless Authentication (JWT Access & Refresh tokens) + Notifications service fixes

[gr4yha7]

Description

Implemented a production-ready authentication system featuring stateless JWTs with token rotation and bcrypt-secured PIN storage.

Key Features

• Stateless Dual-Token System: Separate Access (24h) and Refresh (7d) tokens with token_type claim validation.
• bcrypt PIN Hashing: All authentication PINs are secured using bcrypt with the default cost factor (12).
• Ergonomic Middleware: Introduced the AuthenticatedUser extractor for Axum handlers, simplifying user ID access from request.
• Database Integrity: Added pin_hash migration and resolved critical UUID/String serialization mismatches in the identity and notification services.
• Enhanced Type Support: Enabled "with-serde_json-1" feature for tokio-postgres to support JSONB metadata in notifications.

Issues:

Closes #7.

[gr4yha7]

@anonfedora PR updated.

[anonfedora]

LGTM🚀