refactor(qconnect): route liveness/lifecycle/diagnostic emits through event sink (slice 3)

Add five QconnectAppEvent variants (RendererUnreachable, RendererDisconnected,
ResyncComplete, LifecycleChanged, Diagnostic) and a Tauri mapper so the
session/liveness/diagnostic signals flow through the QconnectEventSink trait
instead of raw app_handle.emit calls. Move QconnectLifecycleState into
qconnect-app (pure data); Tauri types.rs re-exports it for the command surface.

No logic moves: the session logic still lives Tauri-side but now calls
sink.on_event(variant) at each rewired emit site. The sink mapper turns each
variant back into the exact same qconnect:* channel + payload, so the Svelte
wire surface is byte-identical. Each dedicated channel still fires exactly once
per occurrence (raw emits are replaced, not duplicated). The blanket
qconnect:event emit now also carries the new variants, which is additive and
ignored by the Svelte listener (pattern-matches known keys only).

Rewired emit sites:
- event_sink.rs freeze helper now takes/emits the freeze variant
  (RendererUnreachable/RendererDisconnected); the mapper emits the dedicated
  channel. State mutation precedes on_event and the variant arms only emit, so
  there is no re-entrancy/recursion into the watchdog/session dispatch.
- service.rs resync-complete -> ResyncComplete; inbound_queue_event/cloud_error/
  max_reconnect -> Diagnostic; update_lifecycle_state_if_running -> LifecycleChanged.

Tests: add qconnect-app unit tests asserting the new variants flow through a
sink and that QconnectLifecycleState serializes snake_case (matching the wire
payload). crates green (qconnect-app 33 passed); src-tauri cargo test qconnect
42 passed.

cc

crates/qconnect-app/src/lib.rs

@@ -16,8 +16,9 @@ pub use error::QconnectAppError;
 pub use events::{NoOpEventSink, QconnectAppEvent, QconnectEventSink};
 pub use session::{
     compute_connection_state, deferred_join_reason, quality_from_max_audio_quality,
-    should_arm_renderer_watchdog, should_reask_queue_state, ConnectionDecision, RendererStatus,
-    ServerActiveState, JOIN_SESSION_REASON_CONTROLLER_REQUEST, JOIN_SESSION_REASON_RECONNECTION,
+    should_arm_renderer_watchdog, should_reask_queue_state, ConnectionDecision,
+    QconnectLifecycleState, RendererStatus, ServerActiveState,
+    JOIN_SESSION_REASON_CONTROLLER_REQUEST, JOIN_SESSION_REASON_RECONNECTION,
     QCONNECT_RENDERER_LOST_TIMEOUT_MS,
 };
 pub use feature_flags::{