Restructure step 1: lasting identity, presence and protocol 16

Server and core: version ranges on both sides with a coded refusal; a
client id maps to the same member and token for the server's life; a
drop is `gone` for a 10-minute grace keeping ready, presence, queue
items, relay and avatar; `bye` leaves at once; ordered takeover (seq,
replaced/stale); presence joining/in/away/gone with one PresencePolicy;
joiners never pause playback and hold a held gate at most ~15 s;
state.hold; feed ids, seq and replay; the relay lives through its
source's grace and continues on re-dial; queue `by` lasting, auto
items and cancel; MediaRef carried; client ids never logged.

App: persisted client id and seq; Connection with unstable/lost/
replaced states, backoff with jitter, no lost/back pair per flap; a drop
keeps the session (state, player, media, relay source); presence in the
strip and members card; sit out = away intent; feed matched by id;
auto sit-out (idle when not playing, minimised for a while; never when
alone) replaces auto-unready; bye on close and Leave, not on update
restart; relay source re-dials through its grace.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/test/settings_schema_test.dart

@@ -16,10 +16,26 @@ void main() {
       await dir.delete(recursive: true);
     });
 
-    test('a box without a version is at 1 and gets stamped', () async {
+    test('a box without a version is at 1, runs the steps and gets stamped', () async {
       final box = await Hive.openBox('settings');
-      expect(await migrateSettings(box), isEmpty);
+      expect(await migrateSettings(box), hasLength(settingsSchemaVersion - 1));
       expect(box.get(settingsSchemaKey), settingsSchemaVersion);
+      expect(await migrateSettings(box), isEmpty);
+    });
+
+    test('2: the idle switch gives way to auto sit-out, on', () async {
+      for (final old in [true, false]) {
+        final box = await Hive.openBox('settings');
+        await box.put('idleSitsOut', old);
+        await migrateSettings(box);
+        expect(box.containsKey('idleSitsOut'), isFalse);
+        expect(box.get('autoSitOut'), isTrue);
+        await box.deleteFromDisk();
+      }
+      final kept = await Hive.openBox('settings');
+      await kept.putAll({'idleSitsOut': true, 'autoSitOut': false});
+      await migrateSettings(kept);
+      expect(kept.get('autoSitOut'), isFalse, reason: 'a choice already made stays');
     });
 
     test('steps run in order, only past the stored version', () async {