Let players voluntarily leave a game

Adds a "🚪 Leave Game" option to the corner menu for every player, so someone
who's done can remove themselves instead of waiting for an admin to kick them.

leave_game reuses the kick mechanics (cards to discard, reference cleanup,
phase re-check) via a shared _remove_player helper; it logs a friendlier
"left the crew" event and, like kick, refuses the last Admin so the table
isn't orphaned. The self-service route POST /game/{gid}/player/{pid}/leave
lives next to join and authenticates on the player's own id (no admin key).
The handler confirms, forgets the saved session, and routes home.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pirats/main.py

@@ -1,7 +1,7 @@
 from contextlib import asynccontextmanager
 from typing import Optional
 from fastapi import FastAPI, Form, Depends, HTTPException, APIRouter, WebSocket, WebSocketDisconnect
-from fastapi.responses import FileResponse
+from fastapi.responses import FileResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
 from sqlmodel import Session
 import re
@@ -76,6 +76,18 @@ def join_game_submit(
     player = crud.add_player(db, game_id, name.strip(), is_creator=is_creator)
     return {"id": player.id}
 
+@api.post("/game/{game_id}/player/{player_id}/leave")
+def leave_game_route(game_id: str, player_id: str, db: Session = Depends(get_session)):
+    """A player voluntarily removes themselves from the game (counterpart to join)."""
+    game = crud.get_game(db, game_id)
+    player = crud.get_player(db, player_id)
+    if not game or not player or player.game_id != game.id:
+        raise HTTPException(status_code=404, detail="Game or Player not found")
+    ok, msg = crud.leave_game(db, game, player)
+    if not ok:
+        return JSONResponse({"error": msg}, status_code=400)
+    return {"status": "ok"}
+
 @api.get("/game/{game_id}/player/{player_id}/state")
 def get_game_state(game_id: str, player_id: str, db: Session = Depends(get_session)):
     game = crud.get_game(db, game_id)