Publish and pause devices started or stopped while connected

[Magmusacy]

Stacked on #612.

Description

startMicrophone() / startCamera() and stopMicrophone() / stopCamera() now update the published track while connected, the same way toggleMicrophone() / toggleCamera() do.

• Start while connected: publishes the device, or replaces the published track if there is one.
• Stop while connected: stops the device immediately, then pauses the published track (paused: true).
• toggleDevice now reuses the same start and stop logic, so the two paths can't drift apart.
• Not connected: unchanged. A device started before joining is still published on joined; stopping after leaveRoom() sends nothing.

Motivation and Context

Start and stop only touched the local device, so the room fell out of sync:

• stop, then start: the stopped track stayed published, so others heard silence for the rest of the call while the app showed the mic as on;
• stop: others still saw the device as not paused;
• start after joining: nothing was published.

On mobile, where muting is done by stopping the microphone, this made unmuting leave the user silent.

Checked:

• startStopDeviceWhileConnected.spec.ts: 7 tests fail before the change, all 10 pass after; the full react-client suite passes.
• On an Android emulator in a sandbox room: before, the sender kept the ended track after stop then start; after, stop paused the track and start put the live microphone back on the same published track.

Documentation impact

• Documentation update required
• Documentation updated in another PR
• No documentation update required

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)

[linear]

FCE-3857

[Magmusacy]

Parked for now, tracked in FCE-3857. Branch kept.