Start voice polling after session creation

[JulioMCruz]

What changed

• store the created voice session in React state after createVoiceSession returns
• activate session polling from that state while retaining refs for cancellation and cleanup
• add a controller regression test proving joined transitions to in-call and exposes End call
• document the polling lifecycle

Root cause

The polling effect read only sessionRef.current. Session creation populated the ref after the connecting render, but ref assignment did not trigger another render, so the effect never restarted.

Validation

• typecheck passed
• ESLint passed on changed TypeScript files
• 3 focused suites / 5 tests passed
• production build generated all 51 routes with non-secret placeholder Firebase values
• diff and secret scans passed

No real call, credential operation, or deployment occurred.