refactor(qconnect): move loop helpers to qconnect-app (slice 5)

Relocate the transport-loop helpers out of the Tauri adapter into QconnectApp
methods + qconnect-app free items, so the shared session loop (slice 5.2) and a
future Slint adapter use one definition:

- QconnectApp::capture_session_state_takeover_input (locks self.sync)
- QconnectApp::clear_pending_if_matches (locks self.state)
- QconnectApp::send_set_active_renderer  -- inline {"renderer_id": i32} payload,
  byte-identical to the prior QconnectSetActiveRendererRequest serialization
- QconnectApp::ask_for_active_renderer_state / QconnectApp::ask_for_queue_state
- SessionStateTakeoverInput struct + queue_payload_track_preview (pure free fn)

Deleted the service.rs free fns (capture_session_state_takeover_input,
send_set_active_renderer_via_app, ask_for_active_renderer_state,
ask_for_queue_state, queue_payload_track_preview, clear_pending_if_matches) and
the SessionStateTakeoverInput struct; rewired every call site (the loop +
deferred_renderer_join + the reconnect/lagged paths) to the methods. The request
structs serialize identically to the inline json!, so the wire is unchanged.

qconnect-app 38 green, src-tauri qconnect 42 green.

cc

crates/qconnect-app/src/lib.rs

@@ -11,7 +11,9 @@ mod state;
 pub mod startup;
 mod sync_state;
 
-pub use app::{QconnectApp, SessionApplyOutcome};
+pub use app::{
+    queue_payload_track_preview, QconnectApp, SessionApplyOutcome, SessionStateTakeoverInput,
+};
 pub use startup::{compute_effective_startup, QconnectStartupMode};
 pub use error::QconnectAppError;
 pub use events::{NoOpEventSink, QconnectAppEvent, QconnectEventSink};