Address two review comments:
1. (useRealtimeDictation.ts) Increment activeRunIdRef immediately in the
manual-commit cleanup path so late transcript events from the 3s grace
window are rejected by handleRealtimeEvent. Previously, the run stayed
valid during the timeout, allowing transcripts to write back into the
composer after a send, edit-save, or navigation.
2. (transcribe.rs) Replace as_object_mut().unwrap() with a branch that
builds the correct JSON literal directly. Avoids introducing an unwrap
in a production path per AGENTS.md rules.