Mythic Masters walk together: the room checks a den's creature and level against the world seed #3700

Left over from the walking-together climb (#3699 and the rounds before it; code in #3669 and #3676).

Today the Region Durable Object checks a reported den only for whether it fits (denNear and plausible in apps/mythic-masters/src/net/party.ts):

• the den is near the pose the room last relayed for that player;
• the fight report matches the den's creature and level;
• the fight's length fits the time since;
• at most six reports per den.

But the creature and level are whatever the page said when it walked into the den. A page that lies about both passes the check.

The fix: have the room work them out itself, from the same seeded world the page uses. The page gets a wild den's creature and level from wildsNear in src/world/world.ts: hash(cx, cz, 46) over the region's pool, then wildLevel plus the tier's level. The question is how much of world.ts the Worker can carry. It needs the region owner grid and the pools, not the terrain. Either split out a small dens.ts the edge can import, or precompute a table at build time. Measure the Worker bundle before and after, since the Workers size limit applies. Trail dens (trailWilds) and lairs (HUNTS) need the same treatment.

Done when a fought report for a creature or level the den doesn't hold is dropped, with a test per den kind, and the edge bundle stays small.