UI-POLISH-1: namenlose Tiere + Leerwert-Konsistenz

- de.ts: nameless = '(ohne Namen)' (neuer Platzhalter-String)
- GerbilsPage: g.name || t.nameless in Karten-Name + Checkbox-Aria
- GerbilDetailPage: g.name || nameless im h2-Header; g.causeOfDeath/notes via || null (leer-string-sicher wie Herkunft)
- AnimalPicker: g.name || nameless im Picker-Button

e2e: +1 nameless-stub in mock-data; 2 neue Tests (Liste + Detail-Header)

Gate: vitest 82/82, e2e 130/130, tsc clean

gerbil-manager-web/e2e/mock-data.ts

@@ -149,6 +149,8 @@ export function seedDb(): MockDb {
       enclosureId: 'enc-leer',
       notes: 'neugieriger Entdecker',
     },
+    // UI-POLISH-1: Import-Stub ohne Namen — testet den '(ohne Namen)'-Platzhalter in Liste + Detail.
+    gerbil('nameless-stub', '', 'male', '2023-01-01', null, null),
   ]
 
   const litters: Litter[] = [