[backport rh-test] Add session cookie auth (#6299)

## Summary
Backport of session cookie authentication implementation from main to
rh-test.

## Changes
- Added session cookie management via extension hooks
- Cookie created on login, refreshed on token refresh, deleted on logout
- New extension hooks: `onAuthTokenRefreshed()` and `onAuthUserLogout()`
- DDD-compliant structure with platform layer
(`src/platform/auth/session/`)

## Conflict Resolution
- Resolved import conflict in `firebaseAuthStore.ts` (merged
`onIdTokenChanged` + `sendEmailVerification`)
- Added `onIdTokenChanged` mock to tests

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6299-backport-rh-test-Add-session-cookie-auth-2986d73d365081238507f99ae789d44b)
by [Unito](https://www.unito.io)

tests-ui/tests/store/firebaseAuthStore.test.ts

@@ -64,6 +64,7 @@ vi.mock('firebase/auth', async (importOriginal) => {
     createUserWithEmailAndPassword: vi.fn(),
     signOut: vi.fn(),
     onAuthStateChanged: vi.fn(),
+    onIdTokenChanged: vi.fn(),
     signInWithPopup: vi.fn(),
     GoogleAuthProvider: class {
       addScope = vi.fn()