Fix checks job failure by ensuring papers table is present in test DB path

[Copilot]

The checks workflow failed in paper/session tests because queries against papers executed before the table existed in CI. This PR aligns the DB initialization path so the papers schema is consistently created before ingest/session flows run.

• Root cause

  • CI test execution reached paper ingest/session code with a DB state missing papers, causing UndefinedTable and cascading assertion failures.

• Schema/bootstrap alignment

  • Updated the database initialization/migration path used in tests so papers is created in the same startup path CI exercises.
  • Removed the mismatch where some test flows depended on runtime access to papers without guaranteeing table creation first.

• Paper/session flow stability

  • Kept behavior unchanged for existing paper/session logic; the fix is scoped to ensuring required schema availability at execution time.

-- representative schema guard introduced in init/migration path
CREATE TABLE IF NOT EXISTS papers (
  id UUID PRIMARY KEY,
  source TEXT NOT NULL,
  external_id TEXT NOT NULL,
  title TEXT,
  ...
);

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