feat: add hold timer for timed exercises with full sync support

- Play/Stop button replaces checkmark for duration-only exercises
- Green countdown bar with auto-completion and rest timer chaining
- Display duration in seconds (SEC) instead of minutes for holds
- ActiveWorkout model now preserves distance/duration fields on sync
- Hold timer state syncs across devices via SSE
- Workout summary shows per-set hold times for duration exercises
- Template diff compares and displays duration changes correctly

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.25.3",
+	"version": "1.26.0",
 	"private": true,
 	"type": "module",
 	"scripts": {