fix(db): recreate probe_data column as NOT NULL with empty string default

The probe_data column was added with DEFAULT NULL in migration
20260307175815, which causes sql.Scan errors when reading into Go
string fields. This migration drops and recreates the column with
DEFAULT '' NOT NULL to prevent NULL scan errors.

db/migrations/20260309120007_fix_probe_data_null.go

@@ -0,0 +1,28 @@
+package migrations
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/pressly/goose/v3"
+)
+
+func init() {
+	goose.AddMigrationContext(upFixProbeDataNull, downFixProbeDataNull)
+}
+
+func upFixProbeDataNull(_ context.Context, tx *sql.Tx) error {
+	// Recreate probe_data column as NOT NULL with empty string default.
+	// The previous migration created it with DEFAULT NULL, which causes
+	// scan errors when reading into Go string fields.
+	_, err := tx.Exec(`ALTER TABLE media_file DROP COLUMN probe_data`)
+	if err != nil {
+		return err
+	}
+	_, err = tx.Exec(`ALTER TABLE media_file ADD COLUMN probe_data TEXT DEFAULT '' NOT NULL`)
+	return err
+}
+
+func downFixProbeDataNull(_ context.Context, tx *sql.Tx) error {
+	return nil
+}