Save workspace artifacts: character-controller, gdextension scaffold, network scripts, map-pipeline, server config

Includes code from task workspaces that was never pushed:
- client/characters/ — fps_character_controller.gd (400 lines), fps_camera.gd, input_handler.gd
- gdextension/simulation/ — C++ GDExtension scaffold: entity, movement, hit detection, simulation server, state serializer, bitstream (14 files)
- scripts/network/ — ENet-based network_manager.gd, server/client_main.gd, player.gd
- scripts/map_packaging/ — PCK pipeline: pack_map.gd, map_downloader.gd, map_registry_server.py, README
- scripts/config/ — server_config.gd (480 lines)
- scenes/ — client_main, server_main, player, test_range
- project.godot, export_presets.cfg

scenes/server/server_main.tscn

@@ -0,0 +1,14 @@
+[gd_scene load_steps=3 format=3 uid="uid://server_main"]
+
+; Headless dedicated server entry point.
+; Instances the grey-box test map and manages connected players.
+
+[ext_resource type="Script" path="res://scripts/network/server_main.gd" id="1_server_main"]
+[ext_resource type="PackedScene" uid="uid://test_range_map" path="res://scenes/map/test_range.tscn" id="2_test_map"]
+
+[node name="ServerMain" type="Node"]
+script = ExtResource("1_server_main")
+server_port = 34197
+
+[node name="TestMap" type="Node" parent="."]
+; Map is instanced on _ready() by server_main.gd when map_scene is provided.