static-web-server's default cache-control sends max-age=31536000 (1 year)
for .js files but only 1 day for .wasm. After redeployment, Cloudflare CDN
serves the cached old .js with a fresh .wasm, causing EM_ASM address table
mismatches and runtime crashes. Disable built-in cache headers at the origin
so Cloudflare respects new content on each deploy.
Also update AGENTS.md: add deploy commands, fix emsdk path, document the
Cloudflare cache-purge requirement, and correct stale MAX_ENTITY_SPAWNS
and MAX_EXIT_ZONES values.
Replace warm brown asteroid sprites with cold grey cratered moonrock
using irregular silhouettes and crater detail. No burning/fire trail
since there is no atmosphere on the moon — trail is now grey dust
debris. Ground impact uses a 4-layer explosion: rock shrapnel, dust
plume, ground-level dust spread, and a brief white flash. Player-hit
also gets shrapnel + dust cloud instead of the old small puff.
