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)

client/template/world_environment.tres

@@ -0,0 +1,18 @@
+[gd_resource type="Environment" format=3 uid="uid://bqp54syxqnqww"]
+
+[sub_resource type="ProceduralSkyMaterial" id="ProceduralSkyMaterial_cotvt"]
+sky_top_color = Color(0.160784, 0.482353, 0.827451, 1)
+sky_horizon_color = Color(1, 1, 1, 1)
+sun_angle_max = 114.44
+
+[sub_resource type="Sky" id="Sky_prubo"]
+sky_material = SubResource("ProceduralSkyMaterial_cotvt")
+
+[resource]
+background_mode = 2
+sky = SubResource("Sky_prubo")
+sdfgi_use_occlusion = true
+fog_light_color = Color(0.823529, 0.807843, 0.729412, 1)
+fog_light_energy = 0.66
+fog_sky_affect = 0.463
+volumetric_fog_emission = Color(0.266667, 0.266667, 0.266667, 1)