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>

matchmaking-api/app/routers/ranks.py

@@ -0,0 +1,35 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.models import Player
+
+router = APIRouter(prefix="/ranks", tags=["ranks"])
+
+# Mirrors RANK_DATA in spacewar/menu/main_menu.gd — keep the tier names (and
+# ideally thresholds) in sync if either side changes.
+_TIERS: list[tuple[int, str]] = [
+    (0, "CADET"),
+    (1000, "PILOT"),
+    (1400, "ACE"),
+    (1800, "COMMANDER"),
+    (2200, "ADMIRAL"),
+    (2600, "LEGEND"),
+]
+
+
+def _tier_for(mmr: int) -> str:
+    tier = _TIERS[0][1]
+    for threshold, name in _TIERS:
+        if mmr >= threshold:
+            tier = name
+    return tier
+
+
+@router.get("/{callsign}")
+async def get_rank(callsign: str, db: AsyncSession = Depends(get_db)) -> dict:
+    player = (await db.execute(select(Player).where(Player.callsign == callsign))).scalars().first()
+    if player is None:
+        raise HTTPException(status_code=404, detail="Player not found")
+    return {"callsign": player.callsign, "mmr": player.mmr, "rank": _tier_for(player.mmr)}