Centralize predictions ↔ prediction_review join in a view or helper

[jss367]

Context

After #636, every read site that wants prediction review state has to repeat the same incantation:

LEFT JOIN prediction_review pr_rev
  ON pr_rev.prediction_id = pr.id AND pr_rev.workspace_id = ?
WHERE COALESCE(pr_rev.status, 'pending') != 'rejected'

#644 is sweeping remaining sites for the related (detector_confidence, labels_fingerprint) filters, but #636 already needed 19 review rounds to find them all, and #644 is at least one more pass. The cost is structural: any future caller that forgets the join + COALESCE will silently surface rejected rows from another workspace.

Fix

Two options:

Option A — SQL view.

CREATE VIEW predictions_for_workspace AS
SELECT pr.*,
       COALESCE(rv.status, 'pending') AS review_status,
       rv.individual, rv.group_id, rv.vote_count, rv.total_votes
FROM predictions pr
LEFT JOIN prediction_review rv
  ON rv.prediction_id = pr.id AND rv.workspace_id = :ws

Tradeoff: SQLite doesn't support parameterized views, so callers still substitute workspace_id — half the win.

Option B — db.predictions_query(ws_id, ...) helper that returns a callable / pre-built Cursor, used everywhere review-aware reads happen. Easier to test and refactor.

Either way, add a regression test that an intentional-bad query (missing the join) fails so the pattern can't drift back.

Sequencing

Best timed after #644 closes, so the sweep happens once and we centralize a single converged shape.