unify multiple methods of initializing the database schema

> [!NOTE]
> Migrated from [augurlabs/augur#3388](https://github.com/augurlabs/augur/issues/3388)
> Originally opened by `@MoralCode` on 2025-11-10

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One of the challenges is that we have several ways to initialize the schema and they are all different.
- the .sql file you use here is pretty static/independent, likely somewhat dated, and also failed to work when i messed with it as part of my testing (the way it populates data from stdin seemed to be failing)
- replaying the schema migrations (what the Augur CLI does) seems to be the main way, but it requires building augur enough to access alembic and stuff
- creating the schemas from the SQLAlchemy models seem to me missing/not creating some required sequences, making it hard to inititalize things

I want to get these all in sync so that this testing is less fragile in future

_Originally posted by @MoralCode in https://github.com/chaoss/augur/issues/3387#issuecomment-3512811847_