the-robots: gate ammo chests, wire the damage vignette, fix chest fallback

[Noisemaker111]

Fixes the confirmed defects from Noisemaker111/jgengine#1346 in the-robots.

• src/game/commands.ts: openAmmoChest now goes through the same openedChestsStore gate as red chests (claimChest); a re-interact shows CHEST EMPTY and grants nothing.
• src/game/feel.ts, src/loop.ts: notePlayerHealth marks a hurt when the health stat drops between ticks, so DamageVignette renders (noteHurt was never called).
• src/game/world/models.ts: red_chest.fallbackModel → quaternius-modular-scifi/Prop_Crate4 (was dungeon/chest, not in any declared pack).
• src/game/items/weapons/catalog.ts: dropped the unused starterSmg roll.
• src/game/loadouts.ts: starter cash 40 → 50 so one Insta-Health (45) is affordable before the first kill. Assumption: a small nudge is enough; adjust if the economy wants otherwise.
• src/game/commands.test.ts, src/game/feel.test.ts: chests pay out once; health drop marks a hurt, first reading and heals do not.

Not changed: the gun viewmodels are already primitive blasters on main (Viewmodel.tsx), and the unbounded gunRegistry / lastFiredAt maps are left as-is (pruning needs a liveness rule for rolled guns).

Root cause: the ammo chest handler had no once-only gate while the red chest one did; the vignette signal had no producer. Engine side: pickModel accepted a dead fallbackModel silently — a dev warning lands in Noisemaker111/jgengine#1751.

Refs Noisemaker111/jgengine#1346

Verification: bun test src 88 pass (against local 0.18.1 packages; bun install in Games fails on @jgengine/navbake 404 so the workspace typecheck could not run — tsgo on the game reports only the missing vite/client types). drive --spawn -539,0,531.5 --key KeyE twice: reserve 80 → 104 and grenades 2 → 3 after the first press only. drive --spawn -57,0,560 --record: health 80 → 0 under the Rusk aura with the vignette visible on hit frames.

Before / after (starter cash in the HUD):

Damage vignette, frames from the same clip (no hit in the window / hit):

▶ hurt-clip.mp4 (download to play)

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