feat(tier): Erwerb/Kauf je Tier (Datum, Preis, Notiz)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -78,6 +78,8 @@ export interface MockDb {
   namesConfigured: boolean
   // FEEDBACK: "Fehler melden" — gesammelte Berichte (POST /feedback)
   feedback: Record<string, unknown>[]
+  // ERWERB: Erwerb/Kauf je Tier (Kaufdatum, Preis, Notiz) — /acquisitions
+  acquisitions: Record<string, unknown>[]
 }
 
 function gerbil(
@@ -376,5 +378,6 @@ export function seedDb(): MockDb {
     saleAdConfigured: true,
     namesConfigured: true,
     feedback: [],
+    acquisitions: [],
   }
 }