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/lib/codec.ts

@@ -253,6 +253,7 @@ function decodeGameView(g: fb.GameView): GameView {
     lastActivityUnix: Number(g.lastActivityUnix()),
     vsAi: g.vsAi(),
     unreadChat: g.unreadChat(),
+    unreadMessages: g.unreadMessages(),
     seats,
   };
 }
@@ -849,6 +850,7 @@ function emptyGame(): GameView {
     lastActivityUnix: 0,
     vsAi: false,
     unreadChat: false,
+    unreadMessages: false,
     seats: [],
   };
 }