feat: add About Me dialog showing user info, roles, and groups

- Add GET /api/v1/auth/me endpoint returning current user's UserDetail
- Add AboutMeDialog component with role badges and group memberships
- Add userMenuItems prop to TopBar via design-system update
- Wire "About Me" menu item into user dropdown above Logout

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/AboutMeDialog.module.css

@@ -0,0 +1,57 @@
+.loading {
+  display: flex;
+  justify-content: center;
+  padding: 2rem;
+}
+
+.content {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.metaGrid {
+  display: grid;
+  grid-template-columns: auto 1fr;
+  gap: 6px 16px;
+  font-size: 12px;
+  font-family: var(--font-body);
+  margin-bottom: 8px;
+}
+
+.metaLabel {
+  color: var(--text-muted);
+  font-weight: 500;
+}
+
+.metaValue {
+  color: var(--text-primary);
+}
+
+.tagList {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin-top: 4px;
+  margin-bottom: 8px;
+}
+
+.sourceList {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  margin-bottom: 8px;
+}
+
+.sourceNote {
+  font-size: 11px;
+  color: var(--text-muted);
+  font-family: var(--font-mono);
+}
+
+.empty {
+  font-size: 12px;
+  color: var(--text-muted);
+  font-style: italic;
+  font-family: var(--font-body);
+}