Single owner for DB schema; deprecate duplicate init_db in database/db.py

[blinkerbit]

Source: gitlab-issues-export.md (Issue 4)

Weight: 3

Problem / context

aird/database/db.py still defines init_db and tables while runtime uses aird.db.schema. Risk of drift and confused imports (main.py still uses get_data_dir from database/db.py).

Suggested approach / acceptance criteria

• Document canonical module (aird/db/schema.py); mark database/db.py init_db deprecated or thin-wrapper delegating to schema.
• Grep for stray imports; add architecture test if one does not already cover this.
• No behavior change for existing deployments beyond clearer boundaries.