Evaluate migration from SQLite to PostgreSQL

[Mattsface]

Goal

Plan and eventually migrate the application from SQLite to PostgreSQL when the project has a concrete need for it.

Trigger conditions

Revisit this when one or more become true:

• concurrent writers become common
• async/player ingestion increases write pressure materially
• deployment needs a persistent remote database
• SQLite becomes a measured performance or operational bottleneck

Scope when activated

• audit SQLite-specific SQL, migrations, constraints, and transaction assumptions
• verify SQLAlchemy/Alembic compatibility with PostgreSQL
• define a safe data migration path
• add PostgreSQL-backed test coverage for persistence behavior
• preserve ingestion idempotency and DB-only browser requests

Note

This is deferred infrastructure work, not part of M6 or M7. Do not migrate merely for architectural preference; activate it when requirements justify the added operational complexity.