test: Firebase mock harness + createCampaign characterization

- src/__mocks__/firebase/*: jest manual mocks (app/auth/firestore)
- src/__mocks__/firebase/_mock-db.js: in-memory DB + call recorder
- src/setupTests.js: jest-dom, env stubs, crypto polyfill, DB reset
- src/App.characterization.test.js: createCampaign -> setDoc path/payload locked
- src/storage/contract.js (renamed from .test.js, helper not suite)

21 tests green (memory 19 + createCampaign 2).

src/__mocks__/firebase/app.js

@@ -0,0 +1,5 @@
+// jest manual mock: firebase/app
+const fakeApp = { name: '[fake-firebase-app]', options: {} };
+export function initializeApp(config) { return fakeApp; }
+export const getApp = () => fakeApp;
+export const getApps = () => [fakeApp];