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

tools/score_weapons.js

@@ -56,6 +56,7 @@ function accuracy(w) {
 // Total damage in one ammo load (with the same behavior multipliers as DPS).
 function damagePool(w) {
   if (w.ammo === Infinity) return Infinity;
+  if (w.drain) return effectiveDps(w) * (w.ammo / w.drain); // time-denominated magazine
   const perShot = effectiveDps(w) * w.interval;
   return perShot * w.ammo;
 }