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/storage/storage.test.js

@@ -2,7 +2,7 @@
 // TDD: contract = spec. Run against memory first. RED until memory.js built.
 'use strict';
 
-const { runStorageContract } = require('./contract.test');
+const { runStorageContract } = require('./contract');
 const { createMemoryStorage } = require('./memory');
 
 runStorageContract('memory', () => createMemoryStorage());