Add in-game chat, bot fill for casual, and borderless fullscreen

- In-game chat: T=all, Y=team (race doubles as team), server-relayed and
  team-filtered via new ChatManager autoload; last 10 messages shown
  bottom-left (chat/chat_box.gd).
- Bot fill for casual (bots/): keeps each of the match's 2 offered races
  at a minimum of 7 total humans+bots, spawning/despawning reactively as
  players join/leave. Bots always fly their race's fighter and use
  negative peer_ids so they ride the existing networked-ship stack
  (spawning, loadout sync, health/position sync, bullet attribution) with
  no special-casing. Casual matchmaking now forms with just 1 real player
  queued instead of waiting for a second (matchmaking-api/).
- Borderless fullscreen with stretch scaling disabled instead of scaling
  the Steam-Deck-matched 1280x800 canvas up to fill PC monitors (which
  read as zoomed in) — PC monitors now reveal more world/HUD at native
  size instead. Reworked main_menu/team_select/chat_box to position via
  anchors relative to the real window instead of hardcoded coordinates.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

matchmaking-api/app/queue_manager.py

@@ -65,13 +65,12 @@ class QueueManager:
             tickets.sort(key=lambda t: t.queued_at)
         return tickets
 
-    async def _try_form_match(self, mode: Mode, team_size: int, db: AsyncSession) -> None:
-        required = team_size * 2
+    async def _try_form_match(self, mode: Mode, required: int, cap: int, db: AsyncSession) -> None:
         async with self._lock:
             waiting = self._waiting(mode)
             if len(waiting) < required:
                 return
-            group = waiting[:required]
+            group = waiting[:cap]
 
             server = (
                 await db.execute(
@@ -99,8 +98,20 @@ class QueueManager:
         while True:
             await asyncio.sleep(2)
             async with async_session() as db:
-                await self._try_form_match(Mode.casual, settings.casual_team_size, db)
-                await self._try_form_match(Mode.ranked, settings.ranked_team_size, db)
+                # Casual has bot fill (spacewar/bots/bot_manager.gd) — bots pad
+                # both teams up to GameConfig.bot_min_team_size, so a single
+                # queued player is enough to form a match. Still group in
+                # anyone else who queues in the same tick, up to the real
+                # casual_team_size*2 target, rather than capping at 1v1.
+                # Ranked has no bots, so it still needs the full
+                # ranked_team_size*2 real players queued before forming.
+                await self._try_form_match(Mode.casual, required=1, cap=settings.casual_team_size * 2, db=db)
+                await self._try_form_match(
+                    Mode.ranked,
+                    required=settings.ranked_team_size * 2,
+                    cap=settings.ranked_team_size * 2,
+                    db=db,
+                )
 
 
 queue_manager = QueueManager()