Add ENet multiplayer (movement/combat sync) and matchmaking API

Networked play, end to end: connect, get matched, spawn, fight, respawn.

Godot side:
- Replace the single hardcoded Player with per-peer networked ships
  (MultiplayerSpawner + custom spawn_function), driven by client-side
  prediction with server reconciliation for movement.
- Server-authoritative combat: bullets, health, death/respawn all decided
  by the server and broadcast to every peer over RPC.
- Fix a Camera2D bug where Godot auto-promotes the first camera to ever
  enter the scene tree as the active one regardless of its own `current`
  value — with MultiplayerSpawner catch-up replication that was almost
  never the local player's own ship. `make_current()` on the owner's
  camera fixes it; property assignment doesn't reliably override the
  auto-claim.
- Fix two "late joiner never learns already-established state" gaps
  (health, visibility) by folding both into the existing per-tick
  position broadcast instead of relying on one-shot RPCs that only reach
  peers already connected when they fire.
- Make the 2 offered factions in team select match for every player in
  a match: the server decides once and clients either read it directly
  (server's own instance) or request it over RPC, rather than each
  client rolling its own random pair.
- New MatchmakingClient autoload wires the main menu's CASUAL/RANKED
  buttons to the matchmaking API instead of connecting directly.

New matchmaking-api/ (FastAPI + Postgres, Docker Compose):
- Queue/match/stats/ranks endpoints. In-memory matchmaking queue in a
  single API process — no Redis until there's an actual reason to shard
  the queue across instances.
- Background loop forms a match once enough players are queued for a
  mode, assigns the first available registered game server.
- No real server pool yet: one dev server is auto-seeded from
  DEV_SEED_SERVER_IP/PORT; POST /servers/register exists for real
  servers to self-register later but nothing calls it yet.

Docs: CLAUDE.md and overview/tech.md updated to match — networking
checklist mostly checked off, matchmaking backend section rewritten to
describe what was actually built vs. the original Go/Redis plan, and
Current Tasks reordered around what's actually left (bot fill, real
server pool, ranked/MMR refinement, lag compensation).

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

overview/tech.md

@@ -55,19 +55,30 @@ func send_input(dir: Vector2, firing: bool) -> void:
 
 ### Matchmaking Backend
 
-| Component | Tech |
-|-----------|------|
-| API Server | Go or Node.js |
-| Queue / State | Redis |
-| Database (accounts, ranks) | PostgreSQL |
-| Hosting | VPS (Hetzner / DigitalOcean) or self-hosted |
+Built — see `matchmaking-api/README.md` for how to run it. Actual stack
+diverged from the original plan below:
 
-**Flow:**
-1. Client sends "find match" with MMR + mode
-2. Backend queues player, finds lobby within MMR range
-3. Lobby full → backend assigns a game server
-4. Backend sends client the server IP + session token
-5. Client connects directly to game server
+| Component | Planned | Actual |
+|-----------|---------|--------|
+| API Server | Go or Node.js | **FastAPI (Python)** — I/O-bound queue/CRUD logic, not a latency-critical hot path, so dev velocity won over raw throughput |
+| Queue / State | Redis | **In-memory in the API process** — no Redis; revisit only if the API needs to run as more than one instance |
+| Database (accounts, ranks) | PostgreSQL | PostgreSQL, as planned |
+| Hosting | VPS (Hetzner / DigitalOcean) or self-hosted | Not deployed — local Docker Compose only so far |
+
+**Flow (as built):**
+1. Client sends `POST /matchmaking/queue/join` with callsign + mode
+2. Backend queues the ticket; a background loop forms a match once enough
+   players are queued for that mode
+3. Match forms → backend assigns the first available registered `GameServer`
+   for that mode
+4. Client polls `GET /matchmaking/queue/status/{ticket}` until `matched`,
+   then connects directly to the returned server IP/port
+
+Not yet built: session tokens (server IP/port are handed back unauthenticated
+— fine for local dev, not for a real deployment), and a real server pool —
+only one dev server is registered right now (auto-seeded on API startup);
+`POST /servers/register` exists for real servers to self-register/heartbeat
+but nothing calls it yet.
 
 ### Steam Integration
 
@@ -79,11 +90,11 @@ func send_input(dir: Vector2, firing: bool) -> void:
 
 ## Networking Checklist
 
-- [ ] Godot ENet server/client setup
-- [ ] Player input RPC structure
-- [ ] Position sync with interpolation
-- [ ] Ship class registration per peer
-- [ ] Server-authoritative health/death
-- [ ] Matchmaking API (queue + lobby assignment)
+- [x] Godot ENet server/client setup
+- [x] Player input RPC structure
+- [x] Position sync with interpolation
+- [x] Ship class registration per peer
+- [x] Server-authoritative health/death
+- [x] Matchmaking API (queue + lobby assignment) — client wired end-to-end; real server pool and ranked MMR-window widening still open, see Current Tasks in `CLAUDE.md`
 - [ ] GodotSteam auth + VAC
 - [ ] Lag compensation (basic rewind)