Normalize ammo economy: per-weapon refill, stream drain, behavior fixes

- Every special weapon gets an explicit 'refill' (units per ammo pickup,
  tuned so one pickup funds ~10 kills) replacing the ammoRefillFraction
  log2 heuristic and ammoWeight overrides
- Bile Blunderbuss + The Cauterizer join Red Right Hand as time-denominated
  stream weapons ('drain' per second) instead of per-shot cost
- Sawblades ricochet through enemies (bounce fix), traps catch 3 victims,
  lobbed projectiles arc overhead and always trigger at the target point
  (Flesh Masher / Trap Queen / Swarm Jar payloads now actually deploy)
- Boss rooms stock one ammo on entry and drop one guaranteed on death
- Cauterizer burn trimmed (2.2s x2 -> 1.5s x0.8), bile acid pools trimmed
  (3.5s x1.5 -> 2.5s x0.8), Marrow Draught now covers stream drain
- New tools/ammo_sim.js calibrates every weapon into the 8-13 kills/refill
  band (all 15 pass); smoke test guards the ammo structure
- v0.3.0, cache bump v=44

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=43';
+      img.src = 'assets/' + name + '.png?v=44';
     }
   },