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/starlette/background.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+from collections.abc import Callable, Sequence
+from typing import Any, ParamSpec
+
+from starlette._utils import is_async_callable
+from starlette.concurrency import run_in_threadpool
+
+P = ParamSpec("P")
+
+
+class BackgroundTask:
+    def __init__(self, func: Callable[P, Any], *args: P.args, **kwargs: P.kwargs) -> None:
+        self.func = func
+        self.args = args
+        self.kwargs = kwargs
+        self.is_async = is_async_callable(func)
+
+    async def __call__(self) -> None:
+        if self.is_async:
+            await self.func(*self.args, **self.kwargs)
+        else:
+            await run_in_threadpool(self.func, *self.args, **self.kwargs)
+
+
+class BackgroundTasks(BackgroundTask):
+    def __init__(self, tasks: Sequence[BackgroundTask] | None = None):
+        self.tasks = list(tasks) if tasks else []
+
+    def add_task(self, func: Callable[P, Any], *args: P.args, **kwargs: P.kwargs) -> None:
+        task = BackgroundTask(func, *args, **kwargs)
+        self.tasks.append(task)
+
+    async def __call__(self) -> None:
+        for task in self.tasks:
+            await task()