Doom-style weapon audio batch + remove footsteps

- Regenerated all 13 weapon fire one-shots and 4 weapon loops via the audio
  specialist (ElevenLabs) with a 1993 Doom style brief: chunky, bass-heavy,
  crunchy 90s FPS sounds
- New clips wired into SfxBank: ui_active, ui_active_empty (active items),
  ui_curse (legendary pickups, replaces the normal item jingle), plr_revive
  (Second Skin revive)
- Footstep system removed entirely (never worked right): Sfx.footstep, 8
  plr_step* samples and bank entries, player.js call site, smoke test block
- Cache v=42

js/sprites.js

@@ -84,7 +84,7 @@ const Sprites = {
       const img = new Image();
       img.onload = () => { this.imgs[name] = img; if (--pending === 0) G.imagesLoaded = true; };
       img.onerror = () => { if (--pending === 0) G.imagesLoaded = true; };
-      img.src = 'assets/' + name + '.png?v=41';
+      img.src = 'assets/' + name + '.png?v=42';
     }
   },