chore(multiplayer): Phase 0 refactors + graphics/perf settings groundwork

Lands the non-networked Phase 0 tasks from multiplayer-todo.md (ship/camera/
arena refactors, sim constants, background FPS handling) plus a first pass
at exposing graphics/performance settings (presets, resolution scaling,
vsync, FPS cap, perf overlay) and a GPU profiling harness for the
real-hardware follow-up in task 0.15b.

Game/project.godot

@@ -24,16 +24,49 @@ run/main_scene.training="res://scenes/training.tscn"
 
 [autoload]
 
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 GameSettings="*res://scripts/game_settings.gd"
 VideoSettings="*res://scripts/video_settings.gd"
+BackgroundFPS="*res://scripts/background_fps.gd"
+PerfOverlay="*res://scripts/perf_overlay.gd"
 
 [display]
 
 window/size/viewport_width=1920
 window/size/viewport_height=1080
 window/size/mode=2
+; Task 0.17c: kept fixed at "viewport" + 1080p rather than moved to
+; "disabled", deliberately. A player on a 1440p/4K display cannot render
+; native this way, and a 1080p player cannot render lower than 1080p through
+; window scaling alone — but task 0.17b's Viewport.scaling_3d_scale already
+; covers "render lower than the window" independently of stretch mode (it
+; scales the 3D viewport's own internal resolution before this blit, not the
+; window itself), and task 0.15b found an unexplained ~6% non-uniform width
+; scaling on this project's one tested (Mac/Retina) machine — see
+; multiplayer-todo.md §5.5.1 — that needs understanding before stretch mode
+; is touched, not blindly carried into a resolution-dependent change.
 window/stretch/mode="viewport"
 window/stretch/aspect="expand"
+; Task 0.17: default matches VideoSettings.gd's VsyncMode.ADAPTIVE default —
+; VideoSettings.apply_vsync() overwrites this at runtime via DisplayServer as
+; soon as the autoload initializes, so this is only what's in effect for the
+; brief pre-autoload window and if VideoSettings ever fails to load.
+window/vsync/vsync_mode=2
 
 [editor_plugins]
 
@@ -119,6 +152,12 @@ roll_right={
 ]
 }
 
+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)
+]
+}
+
 [layer_names]
 
 3d_physics/layer_1/name="Ships"
@@ -130,9 +169,13 @@ roll_right={
 
 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
+lights_and_shadows/soft_shadow_filter_quality=2