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/pages/FahrzeugBuchungen.tsx

@@ -81,6 +81,7 @@ const EMPTY_FORM: CreateBuchungInput = {
 };
 
 const WRITE_GROUPS = ['dashboard_admin', 'dashboard_fahrmeister', 'dashboard_moderator'];
+const MANAGE_ART_GROUPS = ['dashboard_admin', 'dashboard_moderator'];
 
 // ---------------------------------------------------------------------------
 // Main Page
@@ -89,8 +90,11 @@ const WRITE_GROUPS = ['dashboard_admin', 'dashboard_fahrmeister', 'dashboard_mod
 function FahrzeugBuchungen() {
   const { user } = useAuth();
   const notification = useNotification();
+  const canCreate = !!user;  // All authenticated users can create bookings
   const canWrite =
-    user?.groups?.some((g) => WRITE_GROUPS.includes(g)) ?? false;
+    user?.groups?.some((g) => WRITE_GROUPS.includes(g)) ?? false;  // Can edit/cancel
+  const canChangeBuchungsArt =
+    user?.groups?.some((g) => MANAGE_ART_GROUPS.includes(g)) ?? false;  // Can change booking type
 
   // ── Week navigation ────────────────────────────────────────────────────────
   const [currentWeekStart, setCurrentWeekStart] = useState<Date>(() =>
@@ -194,7 +198,7 @@ function FahrzeugBuchungen() {
   };
 
   const handleCellClick = (vehicleId: string, day: Date) => {
-    if (!canWrite) return;
+    if (!canCreate) return;
     const dateStr = format(day, "yyyy-MM-dd'T'08:00");
     const dateEndStr = format(day, "yyyy-MM-dd'T'17:00");
     setEditingBooking(null);
@@ -339,7 +343,7 @@ function FahrzeugBuchungen() {
             >
               Kalender
             </Button>
-            {canWrite && (
+            {canCreate && (
               <Button
                 startIcon={<Add />}
                 onClick={openCreateDialog}
@@ -442,8 +446,8 @@ function FahrzeugBuchungen() {
                           }
                           sx={{
                             bgcolor: isFree ? 'success.50' : undefined,
-                            cursor: isFree && canWrite ? 'pointer' : 'default',
-                            '&:hover': isFree && canWrite
+                            cursor: isFree && canCreate ? 'pointer' : 'default',
+                            '&:hover': isFree && canCreate
                               ? { bgcolor: 'success.100' }
                               : {},
                             p: 0.5,
@@ -534,7 +538,7 @@ function FahrzeugBuchungen() {
         )}
 
         {/* ── FAB ── */}
-        {canWrite && (
+        {canCreate && (
           <Fab
             color="primary"
             aria-label="Buchung erstellen"
@@ -706,6 +710,7 @@ function FahrzeugBuchungen() {
                 <InputLabel>Buchungsart</InputLabel>
                 <Select
                   value={form.buchungsArt}
+                  disabled={!canChangeBuchungsArt}
                   onChange={(e) =>
                     setForm((f) => ({
                       ...f,