feat(backend): dx improvements

[ivanskv2000]

DX Improvements: Dev Sessions, Auto-Seeding, and Test Users

This PR introduces several quality-of-life improvements for developers:

1. Non-expiring sessions in Dev: JWT access tokens now have a 100-year expiration when running in dev mode, reducing the need for repeated logins.
2. Automated Test Users: A new startup module ensures that user@example.com (password: 12345678) exists on application start in dev mode. This is designed to be easily extendable for future roles.
3. Automatic Database Seeding: The database is now automatically seeded on startup if it's empty (30 events, 12 fields, 7 tags), eliminating the manual seeding step from the UI.

Changes

• backend/app/modules/auth/token.py: Modified create_access_token to handle long-lived dev tokens.
• backend/app/core/startup.py: Added new module for startup tasks (user creation, seeding).
• backend/app/factory.py: Integrated startup tasks into the FastAPI lifespan.

Verification Results

• make format and make lint passed.
• make test passed with 90 tests successful (including new startup tests).
• app/core/startup.py coverage reached 86%.
• Manual verification of auto-seeding logic in dev mode.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud