feat(02-01): refactor ExerciseCard to dynamic setList with add-set modal and delete-set

- Replace fixed setInputs object with setList array state
- Add showAddModal state and set-type chooser modal (Vanligt set / Dropset)
- handleAddNormal: append one set pre-filled from last row's weight and reps
- handleAddDropset: append 3 sets at 100%/80%/60% weight (rounded to 2.5kg), 10 reps
- handleDeleteSet: remove by index with last-set guard (no delete when only 1 remains)
- handleComplete and handleInputChange updated to use array index (idx+1 as set_number)
- Progress badge and all-done class use setList.length instead of exercise.sets
- onDeleteSet prop added (optional stub for backend wiring in plan 02)
- Add trash icon SVG to Icons.jsx (outline trash can, consistent with icon library)

frontend/src/components/Icons.jsx

@@ -216,6 +216,17 @@ export const Icons = {
     </svg>
   ),
 
+  // Actions
+  trash: (
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">
+      <polyline points="3 6 5 6 21 6"/>
+      <path d="M19 6l-1 14a2 2 0 0 1-2 2H8a2 2 0 0 1-2-2L5 6"/>
+      <path d="M10 11v6"/>
+      <path d="M14 11v6"/>
+      <path d="M9 6V4a1 1 0 0 1 1-1h4a1 1 0 0 1 1 1v2"/>
+    </svg>
+  ),
+
   // Brand
   gravl: (
     <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round">