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/model.ts

@@ -51,6 +51,10 @@ export interface GameView {
    *  nudge) in this game. Set on the authoritative REST views (lobby list, game state,
    *  move result); the live-event GameView leaves it false (events bump unread instead). */
   unreadChat: boolean;
+  /** Per-viewer flag: at least one unread entry is a real message (not just a nudge), so the
+   *  badge can be coloured apart from the nudge-only case. Same REST-seeded lifecycle as
+   *  unreadChat; the live-event GameView leaves it false. */
+  unreadMessages: boolean;
   seats: Seat[];
 }