feat: CRUD UI — race form, detail fields, edit/delete actions

- RaceDetailsPage: show all non-null fields (officialUrl, startTime, clusterSchedule, bibPickup)

- RaceDetailsPage: add edit link and delete button with confirmation banner

- RaceFormPage: universal create/edit form with validation, auto-generated id for new races

- Router: add /races/new and /races/:raceId/edit routes

- AppLayout: add navigation link to create new race

- CSS: buttons (primary/secondary/danger), form fields, confirm banner, responsive layout

Made-with: Cursor

frontend/src/styles/global.css

@@ -408,6 +408,175 @@ a {
   color: var(--color-text);
 }
 
+/* ─── Buttons ──────────────────────────────────────────── */
+
+.btn {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  padding: var(--space-2) var(--space-4);
+  border: 1px solid transparent;
+  border-radius: var(--radius-sm);
+  font: inherit;
+  font-weight: 600;
+  font-size: var(--font-size-caption);
+  cursor: pointer;
+  text-decoration: none;
+  white-space: nowrap;
+  transition: background 0.15s, color 0.15s;
+}
+
+.btn:disabled {
+  opacity: 0.55;
+  cursor: not-allowed;
+}
+
+.btn--primary {
+  background: var(--color-accent);
+  color: var(--color-surface);
+}
+
+.btn--primary:hover:not(:disabled) {
+  background: #1766be;
+}
+
+.btn--secondary {
+  background: var(--color-surface);
+  color: var(--color-text);
+  border-color: var(--color-border);
+}
+
+.btn--secondary:hover:not(:disabled) {
+  background: #eef2f6;
+}
+
+.btn--danger {
+  background: var(--color-error);
+  color: var(--color-surface);
+}
+
+.btn--danger:hover:not(:disabled) {
+  background: #a82e2e;
+}
+
+/* ─── Confirm banner ───────────────────────────────────── */
+
+.confirm-banner {
+  margin-top: var(--space-4);
+  padding: var(--space-4);
+  border: 1px solid var(--color-error);
+  border-radius: var(--radius-md);
+  background: #fef2f2;
+}
+
+.confirm-banner__text {
+  margin: 0 0 var(--space-3);
+  font-weight: 600;
+  color: var(--color-error);
+}
+
+.confirm-banner__actions {
+  display: flex;
+  gap: var(--space-3);
+}
+
+/* ─── Race details actions ─────────────────────────────── */
+
+.race-details-actions {
+  margin-top: var(--space-4);
+  display: flex;
+  gap: var(--space-3);
+}
+
+.race-details-meta__link {
+  color: var(--color-accent);
+  word-break: break-all;
+}
+
+.race-details-meta__link:hover {
+  text-decoration: underline;
+}
+
+/* ─── Race form ────────────────────────────────────────── */
+
+.race-form {
+  margin-top: var(--space-6);
+}
+
+.race-form__group {
+  margin: 0 0 var(--space-6);
+  padding: var(--space-5);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius-md);
+  background: #fcfdff;
+}
+
+.race-form__legend {
+  font-size: var(--font-size-body);
+  font-weight: 700;
+  color: var(--color-text);
+  padding: 0 var(--space-2);
+}
+
+.race-form__field {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-1);
+  margin-top: var(--space-4);
+}
+
+.race-form__field:first-of-type {
+  margin-top: var(--space-3);
+}
+
+.race-form__label {
+  font-size: var(--font-size-caption);
+  font-weight: 600;
+  color: var(--color-text-muted);
+}
+
+.race-form__input {
+  font: inherit;
+  padding: var(--space-2) var(--space-3);
+  border-radius: var(--radius-sm);
+  border: 1px solid var(--color-border);
+  background: var(--color-surface);
+  color: var(--color-text);
+}
+
+.race-form__input:focus {
+  outline: 2px solid var(--color-accent);
+  outline-offset: -1px;
+  border-color: var(--color-accent);
+}
+
+.race-form__input--textarea {
+  resize: vertical;
+  min-height: 5rem;
+}
+
+.race-form__actions {
+  display: flex;
+  gap: var(--space-3);
+  align-items: center;
+}
+
+.form-errors {
+  margin: var(--space-3) 0 0;
+  padding: var(--space-3) var(--space-5);
+  border: 1px solid var(--color-error);
+  border-radius: var(--radius-sm);
+  background: #fef2f2;
+  color: var(--color-error);
+  font-size: var(--font-size-caption);
+}
+
+.form-errors__item {
+  margin: var(--space-1) 0;
+}
+
+/* ─── Responsive ───────────────────────────────────────── */
+
 @media (max-width: 900px) {
   .dashboard-grid,
   .race-lists,
@@ -418,4 +587,9 @@ a {
   .race-details-header {
     flex-direction: column;
   }
+
+  .race-form__actions {
+    flex-direction: column;
+    align-items: stretch;
+  }
 }