refactor(site): write generated site outputs into site/prepared

[apresmoi]

What changed

Every generated file the build wrote into the site/ root is now written into site/prepared/, with the same file names.

Generators moved: prepare-catalog, prepare-facilities, prepare-feature-index, prepare-moon-labels, prepare-world-presentation, prepare-shell-icons, prepare-shell-titles, prepare-navigation and prepare-dataset-billboards.

Moved generated files (all ignored, listed in .github/site-refactor.json):

• moon-labels.prepared.json
• prepared-catalogue.mjs, prepared-context-bank-assets.json, prepared-context-json.mts, prepared-context-objects.mts
• prepared-dataset-billboards.json, prepared-dataset-volumes.json, prepared-dot-catalogues.json
• prepared-facilities.json, prepared-feature-index.json, prepared-fit-boxes.json, prepared-hosted-banks.json
• prepared-navigation-markers.mjs, prepared-shell-icons.mjs, prepared-shell-titles.mjs
• prepared-source-credits.json, prepared-sources.json, prepared-stellar-extents.json, prepared-world-presentation.json

Tracked declarations moved with git renames: prepared-catalogue.d.mts, prepared-navigation-markers.d.mts, prepared-shell-icons.d.mts, prepared-shell-titles.d.mts.

Importers, tests, .gitignore, the ESLint ignore, prepare-typecheck, the architecture plan (moves.json, tiers.json) and docs point at the new place. The generated context modules take base: '..' on their globs so their keys, and therefore the built code, are unchanged.

Checks

• Build-comparison lane against a base built from origin/main: L3 semantic and layout equality, 0 differences; L2 server answers identical (preview 352, netlify 350, cloudflare 347, 0 differences); L7 performance guard pass
• pnpm check:architecture
• pnpm typecheck
• pnpm lint
• pnpm test:site: 1752 pass, 0 fail
• Clean preparation (prepare:inputs, prepare:world-presentation, prepare:shell-assets, dataset billboards) from a fresh checkout writes only into site/prepared/; no generated file appears in the site/ root

PR rules