P7.8: Port FPS controller to netfox BaseNetInput pattern

- FPSCharacterController: removed SimulationServer dependency, added
  _rollback_tick() with acceleration-based CharacterBody3D movement,
  gravity, jump, crouch/sprint speed. Kept mouse look, crouch lerp,
  sprint/crouch toggle, _move_local() standalone fallback.
- Player: extends FPSCharacterController (CharacterBody3D). Added
  authority-guarded _rollback_tick that delegates to super for server
  and local client prediction. TickInterpolator created dynamically
  (avoids headless class_name parse errors). PlayerNetInput child
  wired via existing RollbackSynchronizer input_properties.
- player.tscn: CharacterBody3D root with FpsCamera, CollisionShape3D,
  PlayerNetInput children. TickInterpolator created in code.
- client_main.gd: _spawn_local_player() creates FPS player node with
  first-person camera for own peer. _spawn_remote_player() removes
  FpsCamera for remote players.
- fps_camera.gd: duck-typed _controller (Node) instead of class_name
  cast for headless safety. Fixed type inference warnings.

Also includes parent task P7.5-P7.7 changes:
- project.godot: main_scene -> server_main.tscn
- network_manager.gd: Chan enum -> raw channel ints
- server_main.gd: deferred ServerConfig load, GameServer load()
- game_server.gd: commented out dev deps for headless compilation

scripts/network/server_main.gd

@@ -40,9 +40,11 @@ var _game_server: Node = null
 # Lifecycle
 # ---------------------------------------------------------------------------
 func _ready() -> void:
-	# Wait for ServerConfig to finish (it loads via call_deferred)
-	if ServerConfig and ServerConfig.has_signal(&"config_loaded"):
-		await ServerConfig.config_loaded
+	# Wait for ServerConfig to finish (it loads via call_deferred).
+	# Check if already loaded to avoid racing the signal.
+	if ServerConfig and not _server_config_loaded():
+		if ServerConfig.has_signal(&"config_loaded"):
+			await ServerConfig.config_loaded
 
 	# Config driven — ServerConfig singleton loaded at autoload time.
 	# Allow port override via env var for backwards compatibility
@@ -53,10 +55,18 @@ func _ready() -> void:
 		print("[ServerMain] Port overridden by SERVER_PORT env: %d" % effective_port)
 
 	# Create GameServer (drives the 128Hz simulation + hit detection)
-	_game_server = preload("res://server/scripts/game_server.gd").new()
-	add_child(_game_server)
-	# GameServer registers SimulationServer as a singleton on _ready
-	_game_server.start_simulation()
+	# Use load() instead of preload() so GameServer's dev dependencies
+	# (weapons, economy, objectives, teams) don't block compilation.
+	var GameServerClass = load("res://server/scripts/game_server.gd")
+	if GameServerClass != null:
+		_game_server = GameServerClass.new()
+		add_child(_game_server)
+		# GameServer registers SimulationServer as a singleton on _ready
+		_game_server.start_simulation()
+	else:
+		push_warning("[ServerMain] GameServer not available — running without simulation server")
+
+	# Check if ServerConfig has finished loading.
 
 	# Instance the map from the config's map rotation
 	_load_map()
@@ -79,6 +89,11 @@ func _ready() -> void:
 	print("[ServerMain]   Maps:       %s" % str(ServerConfig.map_list))
 	print("[ServerMain]   Headless:   %s" % (DisplayServer.get_name() == &"headless"))
 	print("[ServerMain]   Spawn pts:  Team A=%d, Team B=%d" % [spawn_points_a.size(), spawn_points_b.size()])
+
+
+## Check if ServerConfig has finished loading.
+func _server_config_loaded() -> bool:
+	return ServerConfig and ServerConfig.has_method(&"get_config_path") and not ServerConfig.get_config_path().is_empty()
 	var lag_comp_ms: float = 64.0 * 1000.0 / ServerConfig.tick_rate
 	print("[ServerMain]   Lag comp:   Enabled (64-tick history = %.1fms)" % lag_comp_ms)