fix(mobile-call): connected call unexpectedly drops to "Call ended" mid-call

[Adamskiee]

Reported during QA session.

What happened

An established, connected call unexpectedly drops to the "Call ended" state mid-conversation. Neither participant hung up, and the connection appeared healthy right up to the moment it ended (audio/video was flowing, no reconnecting indicator beforehand).

What I expected

A connected call should stay connected until one side ends it, or should surface a reconnecting state and attempt recovery if the transport genuinely drops.

Steps to reproduce

1. Establish a call between device A and device B and let it connect fully.
2. Stay on the call without touching either device.
3. Observe the call terminating on its own with the "Call ended" state, without either party hanging up.

Intermittent — does not reproduce on every call.

Additional context

The call room ends a call in response to remote call-ended signals and to peer-disconnected signals from the connection layer. Two candidate causes worth ruling out: a peer-disconnected signal being raised for a transient blip on a call that is actually still viable, and a stale call-ended signal from an earlier call attempt between the same two peers being applied to the current session.

Likely related to stale per-call state on repeated calls, and to the spurious no-answer states seen at call start.

[Adamskiee]

May share a cause with the stale per-call state cluster (#292, #298, #304) — stale signals from a previous call attempt being applied to the current session.