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/click/_utils.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+
+import enum
+import typing as t
+
+
+class Sentinel(enum.Enum):
+    """Enum used to define sentinel values.
+
+    .. seealso::
+
+        `PEP 661 - Sentinel Values <https://peps.python.org/pep-0661/>`_.
+    """
+
+    UNSET = object()
+    FLAG_NEEDS_VALUE = object()
+
+    def __repr__(self) -> str:
+        return f"{self.__class__.__name__}.{self.name}"
+
+
+UNSET: t.Literal[Sentinel.UNSET] = Sentinel.UNSET
+"""Sentinel used to indicate that a value is not set."""
+
+FLAG_NEEDS_VALUE: t.Literal[Sentinel.FLAG_NEEDS_VALUE] = Sentinel.FLAG_NEEDS_VALUE
+"""Sentinel used to indicate an option was passed as a flag without a
+value but is not a flag option.
+
+``Option.consume_value`` uses this to prompt or use the ``flag_value``.
+"""
+
+T_UNSET: t.TypeAlias = t.Literal[Sentinel.UNSET]
+"""Type hint for the :data:`UNSET` sentinel value."""
+
+T_FLAG_NEEDS_VALUE: t.TypeAlias = t.Literal[Sentinel.FLAG_NEEDS_VALUE]
+"""Type hint for the :data:`FLAG_NEEDS_VALUE` sentinel value."""