fix: five dashboard improvements across booking, vehicles, profile, and UI

- fix(auth): guard extractNames() against Authentik sending full name in
  given_name field (e.g. "Matthias Hochmeister" + family_name "Hochmeister");
  detect by checking given_name ends with family_name suffix, fall through
  to name-splitting so Vorname/Nachname display correctly in Profile

- fix(db): add migration 018 to repair broken BEFORE UPDATE triggers on
  veranstaltungen and veranstaltung_kategorien; old triggers called
  update_updated_at_column() which references NEW.updated_at, but both
  tables use aktualisiert_am, causing every category/event edit to fail

- feat(booking): open vehicle booking creation to all authenticated users;
  only dashboard_admin / dashboard_moderator can change the Buchungsart
  (type select disabled for regular members); edit and cancel still
  restricted to WRITE_GROUPS

- feat(vehicles): VehicleDashboardCard now fetches equipment warnings via
  equipmentApi.getVehicleWarnings() in parallel and shows an alert when
  any vehicle equipment is not einsatzbereit

- fix(ui): add MuiTextField defaultProps (InputLabelProps.shrink=true) and
  MuiOutlinedInput notch legend font-size override to theme to eliminate
  floating-label / border conflict on click

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/theme/theme.ts

@@ -144,6 +144,22 @@ const lightThemeOptions: ThemeOptions = {
         },
       },
     },
+    MuiTextField: {
+      defaultProps: {
+        InputLabelProps: {
+          shrink: true,
+        },
+      },
+    },
+    MuiOutlinedInput: {
+      styleOverrides: {
+        root: {
+          '& .MuiOutlinedInput-notchedOutline legend': {
+            fontSize: '0.75em',
+          },
+        },
+      },
+    },
   },
 };