feat: integrate ChaffGames FPS template as local player controller

Replaces the overhead box-mesh view with a full FPS character:

- mouse look, WASD movement, jump (Space), crouch (C), sprint (Shift), lean (Q/E)

- 6 weapons (LMB shoot, R reload, scroll switch, F melee, G drop)

- Crosshair HUD, ammo counter, sprint bar

- Client sends position to server at 20Hz for multiplayer visibility

- Server broadcasts positions to all peers

- Remote players shown as boxes (placeholder)

source: https://godotengine.org/asset-library/asset/2652 (MIT license)

scripts/network/server_main.gd

@@ -215,3 +215,23 @@ func _physics_process(delta: float) -> void:
 	
 	# Future: authoritative physics tick, state broadcast, etc.
 	pass
+
+# ---------------------------------------------------------------------------
+# Client position replication (receives from FPS character clients)
+# ---------------------------------------------------------------------------
+@rpc("unreliable", "any_peer")
+func _send_position(pos: Vector3) -> void:
+	# Called by remote clients to update their position on the server.
+	# Broadcast to all other peers so they see the player move.
+	var peer_id: int = multiplayer.get_remote_sender_id()
+	if peer_id in players:
+		players[peer_id].position = pos
+		# Re-broadcast to all other peers
+		_replicate_position.rpc(pos, peer_id)
+
+@rpc("unreliable", "authority")
+func _replicate_position(pos: Vector3, exclude_peer: int) -> void:
+	# All clients receive this and update the specific player's position.
+	# We need to find which remote player this belongs to by excluding our own.
+	# For now, the non-authority clients will need to filter — handled in client_main.gd
+	pass