feat(rust): loot on the NPC profile form, and the Place NPCs step's "drop loot" switch (runicnpc stage 7)

The profile form's Loot section (D290-D301):

- what the corpse starts with (Rust's scientist loot, the kit, or
  nothing);
- rows that always roll, each with its chance;
- a pool capped at its picks, with a "nothing" weight;
- which crate the table goes into, and a locked crate's hack time;
- how long the corpse stays.

The site checks the block as RunicNPC does, in its words. Whether an
item exists on a server is RunicNPC's to say on the push.

The Place NPCs step's dropLoot switch (D296), on by default and sent
only when off.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

server/model/npcs/npcs.model.js

@@ -165,6 +165,8 @@ async function describe() {
     kitUses: shape.KIT_USES,
     announces: shape.ANNOUNCES,
     useModes: shape.USE_MODES,
+    lootStarts: shape.LOOT_STARTS,
+    lootCrates: Object.keys(shape.LOOT_CRATES),
   }
 }