docs: correct stale multiplayer/C#-backend claims, add TECH_STACK doc

CLAUDE.md and README.md described the pre-multiplayer state (local-only
MVP, planned C# backend) even though server-authoritative multiplayer,
the dedicated server, Docker/CI verification, and Steam transport have
since shipped (Phases 1-6). Update both to reflect reality and add a
docs index in CLAUDE.md pointing at multiplayer-next.md as the current
checklist.

- Add docs/TECH_STACK.md, linked from README, explaining the stack and
  why it's a single GDScript project with no separate backend.
- Add one TODO item for the video settings menu (missing presets/vsync/
  resolution scaling), blocked on the same profiling gate as the
  multiplayer 0.17 tasks.
- Pick up editor-generated .gd.uid sidecars and minor project.godot
  formatting noise from opening the project in Godot 4.7.

Game/project.godot

@@ -25,22 +25,6 @@ run/main_scene.dedicated_server="res://scenes/server_boot.tscn"
 
 [autoload]
 
-
-
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-
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-
-
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-
-
-
 GameSettings="*res://scripts/game_settings.gd"
 VideoSettings="*res://scripts/video_settings.gd"
 BackgroundFPS="*res://scripts/background_fps.gd"
@@ -143,7 +127,6 @@ roll_right={
 , Object(InputEventJoypadButton,"resource_local_to_scene":false,"resource_name":"","device":-1,"button_index":10,"pressure":0.0,"pressed":false,"script":null)
 ]
 }
-
 toggle_perf_overlay={
 "deadzone": 0.5,
 "events": [Object(InputEventKey,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"pressed":false,"keycode":0,"physical_keycode":4194334,"key_label":0,"unicode":0,"location":0,"echo":false,"script":null)
@@ -164,15 +147,15 @@ toggle_net_overlay={
 
 [physics]
 
+common/physics_jitter_fix=0.0
 3d/physics_engine="Jolt Physics"
 common/physics_interpolation=true
-common/physics_jitter_fix=0.0
 
 [rendering]
 
-anti_aliasing/quality/msaa_3d=2
-anti_aliasing/quality/screen_space_aa=1
-anti_aliasing/quality/use_debanding=true
-lights_and_shadows/positional_shadow/atlas_size=2048
 lights_and_shadows/directional_shadow/size=2048
+anti_aliasing/quality/msaa_3d=2
+anti_aliasing/quality/use_debanding=true
+anti_aliasing/quality/screen_space_aa=1
+lights_and_shadows/positional_shadow/atlas_size=2048
 lights_and_shadows/soft_shadow_filter_quality=2

Game/scripts/enet_transport.gd.uid

@@ -0,0 +1 @@
+uid://505pjuvqynm0

Game/scripts/net_transport.gd.uid

@@ -0,0 +1 @@
+uid://cjij4dxir0qxd

Game/scripts/steam_bootstrap.gd.uid

@@ -0,0 +1 @@
+uid://itgcxadtf1wd

Game/scripts/steam_transport.gd.uid

@@ -0,0 +1 @@
+uid://c117m546w6u30

Game/tests/cases/test_arena_rotation.gd.uid

@@ -0,0 +1 @@
+uid://cklv8t2htg2gf

Game/tests/cases/test_net_transport.gd.uid

@@ -0,0 +1 @@
+uid://dtqbio4ob00hq

Game/tests/cases/test_project_settings.gd.uid

@@ -0,0 +1 @@
+uid://dvwivtlgx2f34

Game/tests/export_server_smoke.gd.uid

@@ -0,0 +1 @@
+uid://bf7o5x2nug4br

Game/tests/steam_template_smoke.gd.uid

@@ -0,0 +1 @@
+uid://by4f1ydqsm0ry