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/weapons/p90.tres

@@ -0,0 +1,21 @@
+[gd_resource type="Resource" script_class="Weapon" load_steps=4 format=3]
+
+[ext_resource type="Script" path="res://assets/kenney-fps/scripts/weapon.gd" id="1"]
+[ext_resource type="PackedScene" path="res://assets/quaternius/weapons/p90.tscn" id="2"]
+[ext_resource type="Texture2D" uid="uid://ce3lgq7foiusl" path="res://assets/kenney-fps/sprites/crosshair-repeater.png" id="3"]
+
+[resource]
+script = ExtResource("1")
+model = ExtResource("2")
+crosshair = ExtResource("3")
+rotation = Vector3(0, 180, 0)
+muzzle_position = Vector3(0.1, -0.4, 1.5)
+cooldown = 0.08
+max_distance = 15
+damage = 18
+spread = 1.0
+shot_count = 1
+knockback = 10
+min_knockback = Vector2(0.025, 0.025)
+max_knockback = Vector2(0.045, 0.04)
+sound_shoot = "assets/kenney-fps/sounds/blaster_repeater.ogg"