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/quaternius/models/P90.obj.import

@@ -0,0 +1,25 @@
+[remap]
+
+importer="wavefront_obj"
+importer_version=1
+type="Mesh"
+uid="uid://dib3ephrwejf1"
+path="res://.godot/imported/P90.obj-8df31986961b4a8e1ac0386a3807b1da.mesh"
+
+[deps]
+
+files=["res://.godot/imported/P90.obj-8df31986961b4a8e1ac0386a3807b1da.mesh"]
+
+source_file="res://assets/quaternius/models/P90.obj"
+dest_files=["res://.godot/imported/P90.obj-8df31986961b4a8e1ac0386a3807b1da.mesh", "res://.godot/imported/P90.obj-8df31986961b4a8e1ac0386a3807b1da.mesh"]
+
+[params]
+
+generate_tangents=true
+generate_lods=true
+generate_shadow_mesh=true
+generate_lightmap_uv2=false
+generate_lightmap_uv2_texel_size=0.2
+scale_mesh=Vector3(1, 1, 1)
+offset_mesh=Vector3(0, 0, 0)
+force_disable_mesh_compression=false