Clarify self-hosted builds and registry dependencies

[Maya-Kid]

Why

The README describes both build defaults as the GitHub Pages configuration, although SOLID_GLASS_BASE defaults to / and the Pages workflow sets both values explicitly.

What changes

Keep the README to the corrected defaults and a link to the installation page. The self-hosting guide lives only in installation.mdx, with domain-root and subpath examples in one code block, build-time settings, SPA fallback, rebuild requirements, and registry dependency sources. Retain the stylesheet import note so readers use the file's actual installed path.

The final diff changes only README.md and content/docs/installation.mdx. The branch incorporates the current dev through a signed-off merge.

How it was checked

• npm run docs, npm run typecheck, and production builds using both documented deployment commands pass on Node 26.3.0.
• Chromium 155: checked the production installation page in both themes at / and /design/. The README's link resolves to its self-hosting heading, and copying the shared command block preserves the full text. The subpath build was run directly from that copied text.
• Verified all 103 HTML asset references are served with the correct base path, the served registry's own dependencies use the configured site URL, and source-registry dependencies retain their GitHub addresses.
• /dev/examples mounts 389 of 389 examples with 0 failed in each theme and no page errors.

Before review

• Every commit is signed off (git commit -s)
• npm run typecheck and npm run build pass
• /dev/examples reports 0 failed
• What the change touches was looked at in both themes

[WaylandYang]

Thanks, and good catch: the README is wrong. SOLID_GLASS_BASE defaults to /, and only the Pages workflow sets /solid-glass/.

We'd like a smaller change before merging. Right now the same self-hosting guide is written twice, once in the README (+36 lines) and once in installation.mdx, so the two will drift. Suggested split:

• README: just correct the sentence about the defaults (SOLID_GLASS_ORIGIN defaults to the GitHub Pages URL, SOLID_GLASS_BASE to /; the Pages workflow sets both), and link to the installation page for self-hosting.
• installation.mdx: keep the self-hosted registry section there as the one place for it, trimmed a little if you can (the domain-root and subpath examples could share one code block).

The note about adjusting the stylesheet's relative import is useful and can stay as is. Once it's slimmed down we're happy to merge.