Quaternius weapons, input fixes, sound & path fixes

- Added 6 Quaternius weapon models (Pistol, Revolver, Rifle, Shotgun, P90, SniperRifle)
- Created weapon resource files with balanced stats
- Wired Pistol + Rifle into player.tscn replacing Kenney blasters
- Fixed WASD input (matched input map action names)
- Fixed Escape key toggles mouse capture
- Added Audio autoload singleton
- Fixed broken sound asset paths across all scripts
- Fixed all scene ext_resource text paths (nested under assets/kenney-fps/)
- Fixed all .import source_file paths
- Deleted stale .import files (will be regenerated by editor on open)

assets/kenney-fps/sprites/crosshair.png.import

@@ -3,24 +3,18 @@
 importer="texture"
 type="CompressedTexture2D"
 uid="uid://2jld33y6h5pq"
-path.s3tc="res://.godot/imported/crosshair.png-1281ee32d6777347e0f43a202c603c1b.s3tc.ctex"
-metadata={
-"imported_formats": ["s3tc_bptc"],
-"vram_texture": true
-}
+path="res://.godot/imported/crosshair.png-1a2174ba945cb2724603c288af43e347.ctex"
 
 [deps]
 
-source_file="res://sprites/crosshair.png"
-dest_files=["res://.godot/imported/crosshair.png-1281ee32d6777347e0f43a202c603c1b.s3tc.ctex"]
+source_file="res://assets/kenney-fps/sprites/crosshair.png"
+dest_files=["res://.godot/imported/crosshair.png-1a2174ba945cb2724603c288af43e347.ctex"]
 
 [params]
 
-compress/mode=2
+compress/mode=0
 compress/high_quality=false
 compress/lossy_quality=0.7
-compress/uastc_level=0
-compress/rdo_quality_loss=0.0
 compress/hdr_compression=1
 compress/normal_map=0
 compress/channel_pack=0
@@ -28,14 +22,10 @@ mipmaps/generate=true
 mipmaps/limit=-1
 roughness/mode=0
 roughness/src_normal=""
-process/channel_remap/red=0
-process/channel_remap/green=1
-process/channel_remap/blue=2
-process/channel_remap/alpha=3
-process/fix_alpha_border=true
-process/premult_alpha=false
-process/normal_map_invert_y=false
-process/hdr_as_srgb=false
-process/hdr_clamp_exposure=false
-process/size_limit=0
+filter/fix_alpha_border=true
+filter/premult=true
+filter/repeat=true
+filter/filter_clip=false
+filter/anisotropic=0
 detect_3d/compress_to=0
+svg/scale=1.0