refactor(qconnect): relocate pure session/liveness fns to shared crates (slice 0)

Move the frontend-agnostic pure functions and enums out of the Tauri
qconnect adapter into the shared crates, with zero behavior change. The
Tauri side keeps thin re-exports so all existing call sites compile
unchanged.

Into qconnect-app (new `session` module):
  - should_arm_renderer_watchdog
  - compute_connection_state + ServerActiveState + ConnectionDecision
  - deferred_join_reason, should_reask_queue_state
  - RendererStatus + from_wire
  - quality_from_max_audio_quality
  - QCONNECT_RENDERER_LOST_TIMEOUT_MS + JoinSession reason consts

Into qconnect-core (next to evaluate_remote_queue_admission):
  - validate_track_origins_for_admission (pure over TrackOrigin); the
    Tauri command wrapper stays thin and only maps wire origins to core
    origins.

The 6 pure-fn unit tests move into the destination crates' test
modules. R5 honored: compute_connection_state matrix cells are relocated
verbatim, not changed.

cc

src-tauri/Cargo.lock

@@ -5380,6 +5380,7 @@ version = "0.1.0"
 dependencies = [
  "async-trait",
  "log",
+ "qbz-models",
  "qconnect-core",
  "qconnect-protocol",
  "qconnect-transport-ws",