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)

addons/netfox.internals/ring-buffer.gd

@@ -0,0 +1,34 @@
+extends RefCounted
+class_name _RingBuffer
+
+var _data: Array
+var _capacity: int
+var _size: int = 0
+var _head: int = 0
+
+func _init(p_capacity: int):
+	_capacity = p_capacity
+	_data = []
+	_data.resize(p_capacity)
+
+func push(item):
+	_data[_head] = item
+	
+	_size += 1
+	_head = (_head + 1) % _capacity
+
+func get_data() -> Array:
+	if _size < _capacity:
+		return _data.slice(0, _size)
+	else:
+		return _data
+
+func size() -> int:
+	return _size
+
+func is_empty() -> bool:
+	return _size == 0
+
+func clear():
+	_size = 0
+	_head = 0