Introduces shared seams for paginated views, D-pad reorder, media control
routing, async singletons and the device method channel, then points the
open-coded copies at them.
Also removes unused models and duplicated provider/server plumbing, folds
the twice-implemented artifact store in the server, and factors the
repeated Flutter toolchain prologue in CI into a composite action.
Several pairs of near-identical code paths differ in one load-bearing
line. Each site now carries a comment naming the invariant that forces it
apart, backed by a characterization test so a future deduplication fails
loudly instead of silently changing behaviour.
Pinned: focusable wrapper vs. chip D-pad activation policy, profile
connection cleanup's raw-id vs. ServerId-typed server projections, live TV
tab loaders, video player display matching and playback service wiring,
track selection container ordering, tracker HTTP client status ladder, and
the MediaServerHttpClient shutdown/cancellation contract versus
ManagedHttpClient's closing guard.
New tests:
test/focus/dpad_activation_policy_test.dart
test/services/track_selection_container_ordinal_test.dart
test/services/trackers/tracker_status_ladder_test.dart
test/utils/media_server_http_client_shutdown_test.dart
edde746