04-05: Reset to Original feature - custom workouts can be reverted to program versions

- Added reset button (refresh icon) to custom workout cards
- Implemented confirmation dialog to prevent accidental resets
- Integrated with DELETE /api/custom-workouts/:id endpoint
- Added CSS styling: reset button, success message, modal dialog
- Added refresh icon to SVG library
- Frontend build successful

Changes:
- frontend/src/pages/WorkoutSelectPage.jsx (reset flow logic)
- frontend/src/App.css (170 new lines for reset/modal styling)
- frontend/src/components/Icons.jsx (refresh icon)
- Checkpoint updated with task completion metadata

frontend/src/components/Icons.jsx

@@ -261,6 +261,12 @@ export const Icons = {
       <line x1="8" y1="8" x2="16" y2="16"/>
     </svg>
   ),
+  refresh: (
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+      <path d="M1 4v6h6M23 20v-6h-6"/>
+      <path d="M20.49 9A9 9 0 0 0 5.64 5.64L1 10m22 4l-4.64 4.36A9 9 0 0 1 3.51 15"/>
+    </svg>
+  ),
 }
 
 // Icon component wrapper