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>

CLAUDE.md

@@ -27,11 +27,13 @@ README for how to run/extend it.
 5. **Real race art wired in** — Terran Republic, Mechanos Sovereignty, and Vorg Swarm each have their own 5-ship roster (Interceptor/Gunship/Bomber/Support/Heavy) with real sprites cropped from uploaded concept sheets (`assets/images/ships/<race>/`); placeholder `example_ships` removed
 6. **Multiplayer networking (movement + combat)** — ENet authoritative server; networked ship spawning with client-side prediction + server reconciliation for movement; server-authoritative bullets, health, death/respawn all broadcast to every peer (see `overview/tech.md`)
 7. **Matchmaking API + client wiring** — FastAPI + Postgres service (`matchmaking-api/`) for casual/ranked queueing; main menu CASUAL/RANKED buttons queue via the API, poll for a match, then connect to the assigned server. Currently only one dev server is registered (auto-seeded on API startup) — see Current Tasks
+8. **In-game chat** — T focuses "all" chat (whole match, both teams), Y focuses "team" chat (peers sharing the sender's race, since race doubles as team); Enter sends, Esc cancels; last 10 messages shown bottom-left, WoW-style translucent log + input line (`chat/chat_box.gd`); server-relayed and team-filtered via `ChatManager` autoload (`autoload/chat_manager.gd`)
+9. **Bot fill for casual** — each of the match's 2 offered races is kept at a minimum of `GameConfig.bot_min_team_size` (7) total humans+bots; bots spawn/despawn reactively as players join/leave (`bots/bot_manager.gd`, server-authoritative autoload). Bots always fly their race's fighter/Interceptor (`race.ships[0]`) and use negative peer_ids, which lets them ride every existing networked-ship system (spawning, loadout replication, position/health sync, bullet attribution) with zero special-casing. AI (`bots/bot_ai.gd`, `class_name BotAI`) is a simple seek-nearest-enemy-and-shoot brain, deliberately isolated from ship networking code so future tuning/behavior changes stay contained to that one file. See `bots.md`. Casual matchmaking now forms with just 1 real player queued (bots pad the rest) — see `matchmaking-api/README.md`.
+10. **Borderless fullscreen, no UI/world scaling** — launches at the real screen resolution with stretch mode disabled (1 game pixel = 1 screen pixel), instead of scaling the Steam-Deck-matched 1280×800 design canvas up to fill PC monitors (which looked zoomed in). PC monitors now just reveal more world/HUD instead. Every menu screen (`main_menu.gd`, `team_select.gd`, `chat/chat_box.gd`) was reworked to position itself via anchors relative to the real window instead of hardcoded 1280×800 pixel coordinates — see `structure.md`'s Display section, including a real `push_opposite_anchor` footgun hit along the way. `menu/server_browser.gd` was NOT updated (still hardcoded, but unreachable in the live flow).
 
 ## Current Tasks
 
 - [ ] Asteroids and environment hazards
-- [ ] Bot fill for casual (minimum 7v7, bots fill empty slots — see `bots.md`) — next logical step now that matchmaking works, since `CASUAL_TEAM_SIZE` is set low (1) for solo/duo testing on the assumption bots will pad real matches later
 - [ ] Sound effects (thrust, shoot, explosion, UI)
 - [ ] Real game-server pool — servers self-register with the matchmaking API (`POST /servers/register` already exists, nothing calls it yet) instead of one hardcoded dev entry
 - [ ] Galaxy war meta / sector control for casual (see `multiplayer.md`)