feat: sparser robot nudges, typed unread badge, lobby unread bump

Three owner-requested polish changes:

- robot: replace the lengthening 60-90 min -> 6 h proactive-nudge ramp with a
  flat uniform 9-12 h wait before every nudge; the existing sleep-window gate
  still skips and defers a nudge that would land in the robot's night.
- ui: colour the lobby/in-game unread dot by type -- the regular danger colour
  when a chat message is unread, a softer amber (--warn) when only nudges are.
  Adds a per-viewer unread_messages flag (chat_messages.kind='message') across
  the backend DTO, FlatBuffers wire, gateway transcode and the UI store.
- ui: float games with any unread notification to the top of the lobby's
  your-turn and opponent-turn sections (finished keeps its order), reusing the
  existing unread_chat flag.

Docs (ARCHITECTURE 7, FUNCTIONAL + _ru) updated. No DB migration; the new wire
field is backward-compatible.

ui/src/gen/fbs/scrabblefb/game-view.ts

@@ -108,8 +108,13 @@ unreadChat():boolean {
   return offset ? !!this.bb!.readInt8(this.bb_pos + offset) : false;
 }
 
+unreadMessages():boolean {
+  const offset = this.bb!.__offset(this.bb_pos, 32);
+  return offset ? !!this.bb!.readInt8(this.bb_pos + offset) : false;
+}
+
 static startGameView(builder:flatbuffers.Builder) {
-  builder.startObject(14);
+  builder.startObject(15);
 }
 
 static addId(builder:flatbuffers.Builder, idOffset:flatbuffers.Offset) {
@@ -180,12 +185,16 @@ static addUnreadChat(builder:flatbuffers.Builder, unreadChat:boolean) {
   builder.addFieldInt8(13, +unreadChat, +false);
 }
 
+static addUnreadMessages(builder:flatbuffers.Builder, unreadMessages:boolean) {
+  builder.addFieldInt8(14, +unreadMessages, +false);
+}
+
 static endGameView(builder:flatbuffers.Builder):flatbuffers.Offset {
   const offset = builder.endObject();
   return offset;
 }
 
-static createGameView(builder:flatbuffers.Builder, idOffset:flatbuffers.Offset, variantOffset:flatbuffers.Offset, dictVersionOffset:flatbuffers.Offset, statusOffset:flatbuffers.Offset, players:number, toMove:number, turnTimeoutSecs:number, multipleWordsPerTurn:boolean, moveCount:number, endReasonOffset:flatbuffers.Offset, seatsOffset:flatbuffers.Offset, lastActivityUnix:bigint, vsAi:boolean, unreadChat:boolean):flatbuffers.Offset {
+static createGameView(builder:flatbuffers.Builder, idOffset:flatbuffers.Offset, variantOffset:flatbuffers.Offset, dictVersionOffset:flatbuffers.Offset, statusOffset:flatbuffers.Offset, players:number, toMove:number, turnTimeoutSecs:number, multipleWordsPerTurn:boolean, moveCount:number, endReasonOffset:flatbuffers.Offset, seatsOffset:flatbuffers.Offset, lastActivityUnix:bigint, vsAi:boolean, unreadChat:boolean, unreadMessages:boolean):flatbuffers.Offset {
   GameView.startGameView(builder);
   GameView.addId(builder, idOffset);
   GameView.addVariant(builder, variantOffset);
@@ -201,6 +210,7 @@ static createGameView(builder:flatbuffers.Builder, idOffset:flatbuffers.Offset,
   GameView.addLastActivityUnix(builder, lastActivityUnix);
   GameView.addVsAi(builder, vsAi);
   GameView.addUnreadChat(builder, unreadChat);
+  GameView.addUnreadMessages(builder, unreadMessages);
   return GameView.endGameView(builder);
 }
 }