refactor: auth migration and codebase modernization

[7591yj]

Additions

• flake.nix and flake.lock for NixOS development environment
• oidc_auth.py for OIDC authentication
• enums.py to eliminate magic strings
• Logging for routers and alembic/env.py

Changes

• Migrated authentication from Cognito to OIDC
• Migrated to Pydantic v2
• Updated config.py for OIDC and S3-compliant settings
• Consolidated pyproject.toml; removed pytest.ini
• Deduplicated S3 code and admin endpoints
• Removed OtherSettings and Cognito remnants
• Rewrote test suite
• Code formatting and language standardization to English

Fixes

• template.yaml merge conflict
• Logger import failing at module initialization
• Query variable overwriting causing filter loss
• JWKS cache TTL
• Exception chaining; UTC timezone handling
• Pydantic v2 config style
• Lint errors