VadHandler is now the sole mic owner — removed separate AudioRecorder that
caused audio focus contention on Android. Audio from onSpeechEnd is encoded
as WAV for Whisper. Provider switched to autoDispose to match widget lifecycle,
preventing defunct element assertions. Recording UI deferred until mic is open.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Adds discussArticle() to BriefingApi and wires it through to the
RSS news cards in BriefingScreen so tapping Discuss opens a chat
conversation seeded with the article. Also caps RSS cards per
message at 3 to avoid overly long briefing threads.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>