feat(mcp): Rust-owned speaking pill with self-contained audio playback

The pill window now surfaces for agent-initiated speech without main-window
involvement. Rust subscribes to /events/speak via a tokio task + reqwest
streaming body (speak_monitor.rs), shows the pill, and forwards events to
the dictate webview over Tauri's event bus. The pill plays audio via a
plain HTMLAudioElement and emits dictate:hide when playback ends. The
pill stays hidden through the ~1 s generation wait and only surfaces when
audio actually starts, with the counter armed at that moment.

Fixes a shared-dict mutation in mcp_server/events.publish() that caused
the second subscriber (Rust speak_monitor) to receive `event: message`
instead of named speak-start/speak-end frames. Also teaches the speak_monitor
parser to handle CRLF framing (sse-starlette default). Main-window
AudioPlayer now skips autoplay for source in {mcp, rest} to avoid
double-play when both windows are alive.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

backend/routes/generations.py

@@ -237,6 +237,9 @@ async def get_generation_status(generation_id: str, db: Session = Depends(get_db
                     "status": gen.status or "completed",
                     "duration": gen.duration,
                     "error": gen.error,
+                    # Agent-originated sources ("mcp", "rest") skip main-window
+                    # autoplay — the floating pill plays those directly.
+                    "source": gen.source,
                 }
                 yield f"data: {json.dumps(payload)}\n\n"