Add persistence layer to backend

[AdrianoKF]

Major changes

• SQLModel with SQLite database
• Add alembic for migrations, automatically invoked in container
• Pydantic settings for database connection
• Add volume for database persistence in k8s deployment
• Bump pre-commit hooks
• Apply some uv Docker best practices (see https://docs.astral.sh/uv/guides/integration/docker/)
• Support file sync and hot code reload in skaffold dev (removes the need for image build and redeployment in most scenarios)

Settings

Pydantic Settings are used to control behavior of the backend (see config.py). The following settings are currently available:

• AUTO_MIGRATE: bool controls whether Alembic migrations should be automatically applied if the database is out-of-sync
• DB_CONNECTION_STRING: str sets the connection string used to connect to the database

These settings can be passed through environment variables of the same name.

Database Migrations

Alembic is used to perform database migrations.

As part of its entry point script, the container image automatically upgrades to the head revision (alembic upgrade head).

For local development, the AUTO_MIGRATE setting can be used to automatically run migrations on startup (or you can manually use the Alembic CLI).

Tests

The automatic db fixture in the integration test suite provides an in-memory SQLite database session.

---

Closes #133

[codecov]

Codecov Report

Attention: Patch coverage is 73.56322% with 23 lines in your changes missing coverage. Please review.

Project coverage is 57.34%. Comparing base (ff36c96) to head (09fd9b7).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
backend/src/jobq_server/__main__.py	45.00%	11 Missing ⚠️
backend/src/jobq_server/alembic/env.py	80.76%	5 Missing ⚠️
backend/src/jobq_server/db.py	81.48%	5 Missing ⚠️
backend/src/jobq_server/dependencies/__init__.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #138      +/-   ##
==========================================
+ Coverage   56.92%   57.34%   +0.42%     
==========================================
  Files          63       66       +3     
  Lines        3164     3247      +83     
==========================================
+ Hits         1801     1862      +61     
- Misses       1363     1385      +22     

Flag	Coverage Δ
backend	86.51% <73.56%> (-1.68%)	⬇️
client	48.92% <ø> (ø)

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