Fix: Extra DB migration file is created

[hongquan]

In additional to fix of "extra DB migration file keeps being created", this PR also does:

• Use uv as Python package manager.
• Use Ruff to format code.
• Make PostgreSQL the only supported DB.

[sourcery-ai]

Sorry @hongquan, your pull request is too large to review

[norbusan]

Hi @hong_quan Nice idea, but could you please split this into two steps:

• first step does the real code changes (switch to uv, ...)
• second one does the ruff-part
  With the current PR it is impossible to see the actual code changes to switch to ruff/uv are in the middle of all the ruffification.

Aalso, concerning the postgres only change: Please adjust the README.rst to contain a short info/explanation that when running it locally on hte live system (no docker) than one needs to provide a postgres server and set env variables.

Also, the entry DATABASE could be removed from the env.*.sample, and the code in the entrypoint scripts can be simplified to always run the postgres code since it checls for $DATABASE.

So probably the postgres should be a separate PR, too, to be able to be reviewed.

[hongquan]

Close to rework (split to two smaller PRs).