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/screens/Lobby.svelte

@@ -9,6 +9,7 @@
   import { navigate } from '../lib/router.svelte';
   import { t, type MessageKey } from '../lib/i18n/index.svelte';
   import { resultBadge } from '../lib/result';
+  import { badgeKind } from '../lib/unread';
   import { getLobby, setLobby } from '../lib/lobbycache';
   import { preloadGames } from '../lib/preload';
   import { gamePhase, groupGames, shouldBlink, type LobbyPhase } from '../lib/lobbysort';
@@ -35,7 +36,7 @@
       games = list.games;
       // Seed the per-game unread badges from the authoritative list. The live stream only raises
       // unread (it never seeds it from a GameView), so a persisted unread survives a reload here.
-      for (const g of games) seedChatUnread(g.id, g.unreadChat);
+      for (const g of games) seedChatUnread(g.id, g.unreadChat, g.unreadMessages);
       atGameLimit = list.atGameLimit;
       if (!guest) {
         [invitations, incoming] = await Promise.all([gateway.invitationsList(), gateway.friendsIncoming()]);
@@ -75,7 +76,7 @@
   });
 
   const myId = $derived(app.session?.userId ?? '');
-  const groups = $derived(groupGames(games, myId));
+  const groups = $derived(groupGames(games, myId, app.chatUnread));
 
   // Per-card "look here" blink. When a game changes lobby bucket into "your turn" or "finished"
   // while the lobby is on screen, its status emoji blinks twice (an opponent's-turn change is
@@ -253,6 +254,7 @@
           <h2>{t(group.h as 'lobby.yourTurn')}</h2>
           <div class="list">
             {#each group.list as g (g.id)}
+              {@const badge = badgeKind(app.chatUnread[g.id] ?? false, app.messageUnread[g.id] ?? false)}
               <div class="rowwrap" class:revealed={group.finished && revealedId === g.id}>
                 {#if group.finished}
                   <button class="del" onclick={() => hide(g.id)} disabled={!connection.online} aria-label={t('lobby.hideGame')}>❌</button>
@@ -267,7 +269,7 @@
                     <span class="info">
                       <span class="who">
                         <span class="who-name">{opponents(g) || '—'}</span>
-                        {#if app.chatUnread[g.id]}<span class="unread-dot"></span>{/if}
+                        {#if badge}<span class="unread-dot" class:nudge={badge === 'nudge'}></span>{/if}
                       </span>
                       <span class="sub">{scoreline(g)}</span>
                     </span>
@@ -458,7 +460,8 @@
     overflow: hidden;
     text-overflow: ellipsis;
   }
-  /* A small red dot beside the opponent name: this game has an unread chat entry. */
+  /* A small dot beside the opponent name: this game has an unread chat entry. Red for an unread
+     message, a softer amber when only nudges are unread. */
   .unread-dot {
     flex: 0 0 auto;
     width: 8px;
@@ -466,6 +469,9 @@
     border-radius: 50%;
     background: var(--danger);
   }
+  .unread-dot.nudge {
+    background: var(--warn);
+  }
   .sub {
     font-size: 0.85rem;
     color: var(--text-muted);