…ty bubbles

Restructure SharedFlow event handlers to use fire-and-forget pattern
(viewModelScope.launch) for network calls, preventing backpressure from
blocking all event delivery when any gRPC call hangs offline. Capture
text and clear input synchronously on Main thread via flowOn before
launching the send coroutine.

Add 30s gRPC deadline to sendMessage so pending bubbles transition to
FAILED status instead of hanging indefinitely. Add tap-to-retry flow
for failed messages with in-place status update (FAILED→SENDING) to
avoid UI jitter. Guard against blank message sends at both VM and
coordinator layers.

Signed-off-by: Brandon McAnsh <[email protected]>