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)

client/scripts/test_paths.gd

@@ -0,0 +1,42 @@
+extends SceneTree
+
+func _init():
+	print("Current working dir: ", OS.get_executable_path())
+	
+	# List resources in assets/scenes/modular/
+	var dir = DirAccess.open("res://assets/scenes/modular/")
+	if dir:
+		print("Files in res://assets/scenes/modular/:")
+		dir.list_dir_begin()
+		var f = dir.get_next()
+		while f != "":
+			print("  ", f)
+			f = dir.get_next()
+	else:
+		print("Cannot open res://assets/scenes/modular/")
+		print("Error code: ", DirAccess.get_open_error())
+	
+	# Try loading kit_demo
+	var path = "res://assets/scenes/modular/kit_demo.tscn"
+	print("Loading: ", path)
+	var scene = ResourceLoader.load(path)
+	if scene:
+		print("Loaded! Class: ", scene.get_class())
+		var instance = scene.instantiate()
+		print("Instantiate result: ", instance != null)
+		if instance:
+			print("Instance type: ", instance.get_class())
+			print("Instance name: ", instance.name)
+	else:
+		print("Failed to load: ", path)
+	
+	# Try wall_straight_01
+	path = "res://assets/scenes/modular/wall_straight_01.tscn"
+	print("Loading: ", path)
+	scene = ResourceLoader.load(path)
+	if scene:
+		print("Loaded! Class: ", scene.get_class())
+	else:
+		print("Failed to load: ", path)
+	
+	quit(0)