Move the cross-submodule remote-sync accumulator into the new
frontend-agnostic qconnect_app::sync_state module. All field types are
now frontend-agnostic (primitives / qconnect-core / qconnect-app), so
the struct moves cleanly with pub fields; the Tauri qconnect module
re-exports it so existing super::QconnectRemoteSyncState references and
the Arc<Mutex<>> creation/threading in service.rs compile unchanged.
It stays ONE struct under ONE lock by design: capture_session_state_takeover_input
reads session topology together with last_renderer_playing_state, and the
materialize path reads last_renderer_* with last_applied_queue_state, all
atomically. Splitting them would tear the takeover decision, so the whole
accumulator relocates as a unit (single-lock locking is byte-identical).
Two test-only re-exports (find_unique_renderer_id, QconnectSessionRendererState)
are gated #[cfg(test)] since their non-test consumers moved to qconnect-app.
qconnect-app + src-tauri qconnect tests green (33 / 42), no new warnings.
cc
vicrodh
a79971e470