Protocol 15: one shared session log on the server, chat never logged, Mark a problem

Every app streams its redacted diagnostic lines (server time, batched
every 10 s, gzip, buffered while offline) to POST /l/; the server merges
them with its own into session-YYYY-MM-DD.log in time order, tagged by
who. Opt-out in Settings > About; Mark a problem (Ctrl+Shift+B, the
player menus, About) writes a marker with an optional note. Copy
diagnostics can include the server's session log. Chat text never
reaches any log.

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

packages/server/test/session_test.dart

@@ -64,8 +64,8 @@ void main() {
   });
 
   group('core welcome + proto', () {
-    test('proto 14: avatars by hash, profile intent', () {
-      expect(RelayConstants.protoVersion, 14);
+    test('proto 15: avatars by hash, profile intent', () {
+      expect(RelayConstants.protoVersion, 15);
       const v = MemberView(id: 'm1', name: 'a', ready: false, inSet: false, buffered: 0, stale: false);
       expect(v.toJson().containsKey('avatarHash'), isFalse);
       expect(v.toJson().containsKey('avatar'), isFalse);