Phase 7: netfox + godot-jolt stack upgrade

Stack installed:
- netfox v1.35.3 (core + extras + noray + internals)
- godot-jolt v0.16.0-stable

Architecture:
- Server: ENet transport (works headless, no netfox deps)
- Client/Editor: netfox rollback (RollbackSynchronizer, TickInterpolator)

New/modified:
- docs/migration-netfox-plan.md — migration architecture
- scripts/network/network_manager.gd — netfox-aware ENet fallback
- scripts/network/player.gd — clean base player
- client/characters/player_netfox.gd — rollback player w/ WeaponManager
- client/characters/input/player_net_input.gd — BaseNetInput subclass
- client/characters/character/fps_character_controller.gd — netfox input feed
- client/weapons/ — weapon data, registry, TacticalWeaponHitscan, WeaponManager
- client/scripts/round_replicator.gd — client-side round state bridge
- server/scripts/round_manager.gd — improved state machine
- server/scripts/plugin_api/plugin_manager.gd — refined plugin system
- config: enemy_tag, ally_tag for meatball targeting

Removed: old C++ SimulationServer GDExtension (replaced by netfox rollback)

server/server-browser-api/venv/lib/python3.11/site-packages/fastapi/exception_handlers.py

@@ -0,0 +1,34 @@
+from fastapi.encoders import jsonable_encoder
+from fastapi.exceptions import RequestValidationError, WebSocketRequestValidationError
+from fastapi.utils import is_body_allowed_for_status_code
+from fastapi.websockets import WebSocket
+from starlette.exceptions import HTTPException
+from starlette.requests import Request
+from starlette.responses import JSONResponse, Response
+from starlette.status import WS_1008_POLICY_VIOLATION
+
+
+async def http_exception_handler(request: Request, exc: HTTPException) -> Response:
+    headers = getattr(exc, "headers", None)
+    if not is_body_allowed_for_status_code(exc.status_code):
+        return Response(status_code=exc.status_code, headers=headers)
+    return JSONResponse(
+        {"detail": exc.detail}, status_code=exc.status_code, headers=headers
+    )
+
+
+async def request_validation_exception_handler(
+    request: Request, exc: RequestValidationError
+) -> JSONResponse:
+    return JSONResponse(
+        status_code=422,
+        content={"detail": jsonable_encoder(exc.errors())},
+    )
+
+
+async def websocket_request_validation_exception_handler(
+    websocket: WebSocket, exc: WebSocketRequestValidationError
+) -> None:
+    await websocket.close(
+        code=WS_1008_POLICY_VIOLATION, reason=jsonable_encoder(exc.errors())
+    )