feat(02-01): add CSS for add-set button, delete-set button, and set-type modal

- .add-set-btn: full-width dashed border button, 44px touch target, accent hover
- .delete-set-btn: 36px wide inline button, subtle opacity, red on hover, disabled state
- .set-type-modal-overlay: fixed fullscreen overlay with semi-transparent dark background
- .set-type-modal: bottom-sheet card (border-radius top only), max-width 600px
- .set-type-option: full-width option card with label/description layout, 56px tall
- .set-type-option.dropset: accent-colored title for dropset option
- .set-type-cancel: borderless cancel button, 44px touch target
- Uses existing dark theme variables: --bg-card, --bg-secondary, --border, --accent, --text-primary, --text-secondary

frontend/src/App.css

@@ -1911,3 +1911,131 @@ textarea {
     min-height: 48px;
   }
 }
+
+/* Add set button */
+.add-set-btn {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 100%;
+  min-height: 44px;
+  margin-top: 0.5rem;
+  padding: 0.5rem 1rem;
+  background: transparent;
+  border: 1px dashed var(--border);
+  border-radius: 8px;
+  color: var(--text-secondary);
+  font-size: 0.875rem;
+  font-weight: 500;
+  cursor: pointer;
+  transition: border-color 0.15s, color 0.15s;
+}
+
+.add-set-btn:hover {
+  border-color: var(--accent);
+  color: var(--accent);
+}
+
+/* Delete set button */
+.delete-set-btn {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 36px;
+  min-height: 44px;
+  background: transparent;
+  border: none;
+  color: var(--text-secondary);
+  cursor: pointer;
+  opacity: 0.6;
+  transition: opacity 0.15s, color 0.15s;
+  flex-shrink: 0;
+}
+
+.delete-set-btn:hover:not(:disabled) {
+  color: #e53e3e;
+  opacity: 1;
+}
+
+.delete-set-btn:disabled,
+.delete-set-btn.disabled {
+  opacity: 0.2;
+  cursor: not-allowed;
+}
+
+/* Set type modal */
+.set-type-modal-overlay {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.6);
+  display: flex;
+  align-items: flex-end;
+  justify-content: center;
+  z-index: 200;
+  padding-bottom: env(safe-area-inset-bottom, 0);
+}
+
+.set-type-modal {
+  background: var(--bg-card);
+  border-radius: 16px 16px 0 0;
+  padding: 1.5rem 1rem 2rem;
+  width: 100%;
+  max-width: 600px;
+  display: flex;
+  flex-direction: column;
+  gap: 0.75rem;
+}
+
+.set-type-modal h3 {
+  font-size: 1rem;
+  font-weight: 600;
+  color: var(--text-primary);
+  margin: 0 0 0.25rem;
+  text-align: center;
+}
+
+.set-type-option {
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  gap: 0.2rem;
+  width: 100%;
+  min-height: 56px;
+  padding: 0.75rem 1rem;
+  background: var(--bg-secondary);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  cursor: pointer;
+  text-align: left;
+  transition: border-color 0.15s;
+}
+
+.set-type-option strong {
+  font-size: 1rem;
+  color: var(--text-primary);
+}
+
+.set-type-option span {
+  font-size: 0.8rem;
+  color: var(--text-secondary);
+}
+
+.set-type-option:hover {
+  border-color: var(--accent);
+}
+
+.set-type-option.dropset strong {
+  color: var(--accent);
+}
+
+.set-type-cancel {
+  width: 100%;
+  min-height: 44px;
+  padding: 0.75rem;
+  background: transparent;
+  border: none;
+  color: var(--text-secondary);
+  font-size: 0.9rem;
+  cursor: pointer;
+  margin-top: 0.25rem;
+}