Add unit-test coverage for app/sagas/

Background

app/sagas/ has just two existing tests (videoConf.voipBlock.test.ts, deepLinking.test.ts). Core sagas — login.js, init.js, rooms.js, messages.js, encryption.js, state.js, selectServer.ts, room.js — have no direct unit-test coverage.

Motivating example

NATIVE-1180 / #7333 / #7340: an unconditional cancel(loginSuccessTask) in login.js's root() watcher imposed a hard 2-second deadline on handleLoginSuccess and stranded users on the login screen when permission/enterprise fetches ran long. The bug lived in root()'s cancel logic for ~3 weeks before a user reported it.

A small saga harness asserting that cancel(loginSuccessTask) only fires when SERVER.SELECT_REQUEST wins the race would have failed loudly the moment the regression landed.

Suggested scope

• Set up a saga test harness under app/sagas/__tests__/ using runSaga or expectSaga from @redux-saga/testing-utils.
• First pass: cover the root() watcher in login.js — SERVER.SELECT_REQUEST cancels handleLoginSuccess; 2s timeout does not.
• Subsequent passes: high-traffic sagas (init.js, selectServer.ts, rooms.js).

Non-goals

• Not aiming for 100% saga coverage. Pick the seams where regressions are most costly (auth, server switch, deep links, rooms sync).

Start with the existing tests in app/sagas/tests/videoConf.voipBlock.test.ts and deepLinking.test.ts, then inspect app/sagas/login.js and its root() watcher. Set up the suggested runSaga or expectSaga harness and cover the SERVER.SELECT_REQUEST and timeout cases. Done means the root watcher behavior is asserted and the new tests pass.