refactor(model): move the held address reader out of navigation history

[apresmoi]

What changed

• The held address reader (navigationHref and its owner registry) now lives in site/model/navigation-href.mts. Navigation history registers its reader there and re-exports the getter, so existing callers are unchanged.
• World resources reads the address from the model module instead of importing navigation history, which removes an import loop between the world and navigation layers.
• The S3-1 group is retired from the site architecture plan, and .github/site-refactor.json declares the change with layout: "changes".
• Chunk move: history is now reachable only from the scene router, so the bundler moves it from the scene-datasets chunk into the scene-router chunk. scene-router grows 45417 to 50602 raw (+11%) and scene-datasets shrinks by the same amount. Pinning history to its old chunk with manualChunks was tried and made layout and bytes worse, so the plain move ships.

Per-route bytes against main (all 15 measured routes show the same figures per route shape; client JS astro gzip 368634 to 368570):

Route shape	First view gzip	First view brotli	Total loaded gzip	Total loaded brotli	Total loaded raw
/, /earth/, /dione/	325596 to 325524 (-0.02%)	323403 to 323333 (-0.02%)	543975 to 545535 (+0.29%)	539914 to 541510 (+0.30%)	1656584 to 1661829 (+0.32%)
Other routes (raw)	974704 to 974764 (+0.006%)				1654391 to 1659636 (+0.32%)

Total loaded is the first-view closure plus the lazily loaded closure. No route's first view or total grows by more than 0.5%.

Checks

• Local build comparison lane against main: L3 closure-only differences pass (exit 0), L2 server answers identical on preview, Netlify and Cloudflare (0 differences).
• pnpm check:architecture, pnpm typecheck, eslint on the touched files.
• Tests: site/model/navigation-href.test.mts, site/test/navigation-history.test.mts, site/application-world-resources.characterization.test.mts (16 pass).

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