Give items and encounters stable slugs

Every item, loot table, encounter, and pool has a slug: a short, unique name you refer to it by. Flows, scripts, shops, and other tables all point at content through that slug, not through the display name.

Pick a slug once and keep it. Renaming the display name is safe at any time, but changing a slug breaks every reference that pointed at the old one. Treat the slug as an identifier and the name as the label.

A few habits keep slugs tidy: use lowercase words joined by hyphens, keep them short but specific (ember-shard, not item1), and name the thing rather than its rarity, so a Rare item that later becomes Legendary does not end up with a misleading slug.