feat(store): TranscriptStatus read field + status setter/loader

Surfaces videos.transcript_status (migration 007) on SummaryRow and adds
SetTranscriptStatus / GetTranscriptStatus / RateLimitedVideoIDs.

SetTranscriptStatus is the single choke point for the rate-limit lifecycle:
"rate_limited" stamps rate_limited_at = NOW(), every other status clears it,
so the runner's backoff window and the UI badge read one consistent source.
RateLimitedVideoIDs is the per-pass loader (mirrors SeenVideoIDs) the runner
uses to skip still-throttled videos without re-hitting the caption endpoint.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/adapters/store/transcript_status.go

@@ -0,0 +1,102 @@
+package store
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+)
+
+// validTranscriptStatuses bounds SetTranscriptStatus input. "" clears the status
+// (column NULL); the three named states mirror migration 007's documented values.
+var validTranscriptStatuses = map[string]bool{
+	"":             true,
+	"none":         true,
+	"rate_limited": true,
+	"fetched":      true,
+}
+
+// SetTranscriptStatus records the outcome of the last transcript attempt for a
+// video (migration 007). When status is "rate_limited" it also stamps
+// rate_limited_at = NOW() so the runner can back off; every other status clears
+// that timestamp. "" unsets the status (column NULL). An unknown status is
+// rejected. Scoped via withUser, so RLS confines the UPDATE to the caller's own
+// video; ErrNotFound when the user has no such video.
+func (s *Store) SetTranscriptStatus(ctx context.Context, userID, videoID, status string) error {
+	if !validTranscriptStatuses[status] {
+		return fmt.Errorf("store: invalid transcript status %q", status)
+	}
+	return s.withUser(ctx, userID, func(tx pgx.Tx) error {
+		ct, err := tx.Exec(ctx,
+			`UPDATE videos
+			    SET transcript_status = NULLIF($1, ''),
+			        rate_limited_at = CASE WHEN $1 = 'rate_limited' THEN NOW() ELSE NULL END
+			  WHERE id = $2`,
+			status, videoID)
+		if err != nil {
+			return fmt.Errorf("store: set transcript status: %w", err)
+		}
+		if ct.RowsAffected() == 0 {
+			return ErrNotFound
+		}
+		return nil
+	})
+}
+
+// GetTranscriptStatus returns a video's transcript_status ("" when unset/NULL).
+// Returns ErrNotFound when the user has no such video. Scoped via withUser.
+func (s *Store) GetTranscriptStatus(ctx context.Context, userID, videoID string) (string, error) {
+	var status string
+	if err := s.withUser(ctx, userID, func(tx pgx.Tx) error {
+		err := tx.QueryRow(ctx,
+			`SELECT COALESCE(transcript_status, '') FROM videos WHERE id = $1`, videoID).Scan(&status)
+		if errors.Is(err, pgx.ErrNoRows) {
+			return ErrNotFound
+		}
+		return err
+	}); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return "", ErrNotFound
+		}
+		return "", fmt.Errorf("store: get transcript status: %w", err)
+	}
+	return status, nil
+}
+
+// RateLimitedVideoIDs returns the user's videos currently in the "rate_limited"
+// state, mapped to when the 429 was stamped (rate_limited_at). The run loop loads
+// it once per pass (mirroring SeenVideoIDs) to skip re-fetching a video still
+// inside the backoff window, saving caption requests. Scoped by user_id.
+func (s *Store) RateLimitedVideoIDs(ctx context.Context, userID string) (map[string]time.Time, error) {
+	out := make(map[string]time.Time)
+	if err := s.withUser(ctx, userID, func(tx pgx.Tx) error {
+		rows, err := tx.Query(ctx,
+			`SELECT id, rate_limited_at FROM videos
+			  WHERE user_id = $1 AND transcript_status = 'rate_limited' AND rate_limited_at IS NOT NULL`,
+			userID)
+		if err != nil {
+			return fmt.Errorf("store: rate limited video ids: %w", err)
+		}
+		defer rows.Close()
+
+		for rows.Next() {
+			var (
+				id string
+				at time.Time
+			)
+			if err := rows.Scan(&id, &at); err != nil {
+				return fmt.Errorf("store: scan rate limited id: %w", err)
+			}
+			out[id] = at
+		}
+		if err := rows.Err(); err != nil {
+			return fmt.Errorf("store: iterate rate limited ids: %w", err)
+		}
+		return nil
+	}); err != nil {
+		return nil, err
+	}
+	return out, nil
+}