refactor(api): merge review-queue into /api/activities, rename resolve to assign

Removes the unused GET /api/activities list/detail endpoints, moves the
review-queue list and resolve/unlock/unassign actions under
/api/activities, renames resolve to assign end-to-end, and drops the
now-unused store.ReviewQueue helper.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/internal/store/assignments.go

@@ -76,31 +76,6 @@ func (db *DB) CurrentAssignment(ctx context.Context, userID, activityID int64) (
 	return a, true, nil
 }
 
-// ReviewQueue returns userID's activities whose current assignment status
-// is needs_review, newest first.
-func (db *DB) ReviewQueue(ctx context.Context, userID int64) ([]KindAssignment, error) {
-	rows, err := db.QueryContext(ctx, `
-		SELECT `+kindAssignmentColumns+`
-		FROM current_kind_assignment a
-		JOIN activities ON activities.id = a.activity_id
-		WHERE activities.user_id = ? AND a.status = ?
-		ORDER BY a.created_at DESC`, userID, AssignmentStatusNeedsReview)
-	if err != nil {
-		return nil, fmt.Errorf("review queue for user %d: %w", userID, err)
-	}
-	defer rows.Close()
-
-	assignments := []KindAssignment{}
-	for rows.Next() {
-		a, err := scanKindAssignment(rows)
-		if err != nil {
-			return nil, fmt.Errorf("scan kind assignment row: %w", err)
-		}
-		assignments = append(assignments, a)
-	}
-	return assignments, rows.Err()
-}
-
 // AllCurrentAssignments returns the latest assignment for every one of
 // userID's activities that has one, regardless of status or source -- the
 // basis for deciding which activities a global reclassify pass may touch.