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/setuptools/_itertools.py

@@ -0,0 +1,23 @@
+from more_itertools import consume  # noqa: F401
+
+
+# copied from jaraco.itertools 6.1
+def ensure_unique(iterable, key=lambda x: x):
+    """
+    Wrap an iterable to raise a ValueError if non-unique values are encountered.
+
+    >>> list(ensure_unique('abc'))
+    ['a', 'b', 'c']
+    >>> consume(ensure_unique('abca'))
+    Traceback (most recent call last):
+    ...
+    ValueError: Duplicate element 'a' encountered.
+    """
+    seen = set()
+    seen_add = seen.add
+    for element in iterable:
+        k = key(element)
+        if k in seen:
+            raise ValueError(f"Duplicate element {element!r} encountered.")
+        seen_add(k)
+        yield element