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.

pkg/wire/build.go

@@ -46,6 +46,9 @@ type GameView struct {
 	VsAI bool
 	// UnreadChat is a per-viewer flag: the requesting player has unread chat in this game.
 	UnreadChat bool
+	// UnreadMessages is a 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.
+	UnreadMessages bool
 }
 
 // TileRecord is one tile in a decoded MoveRecord (the concrete letter, "?" for a blank
@@ -165,6 +168,7 @@ func BuildGameView(b *flatbuffers.Builder, g GameView) flatbuffers.UOffsetT {
 	fb.GameViewAddLastActivityUnix(b, g.LastActivityUnix)
 	fb.GameViewAddVsAi(b, g.VsAI)
 	fb.GameViewAddUnreadChat(b, g.UnreadChat)
+	fb.GameViewAddUnreadMessages(b, g.UnreadMessages)
 	return fb.GameViewEnd(b)
 }