feat: build the site with Astro Starlight

generate_site.py writes the Starlight project in website/ and nothing
else: mkdocs.yml, the MkDocs hooks, theme overrides and stylesheet go,
and the wiki is written in Starlight's syntax. Both workflows set up
Node with the official actions/setup-node pinned by commit, run npm ci
from the committed lockfile, build with the strict link validator and
check the result with validate_site.py.

The search weighs a page by what it answers: Start here pages first,
a system page's cards and file names before a guide citing them, deep
guides, launchers, aliases and frozen copies after. Status badges,
hash blocks and the export change lists leave the index. The ranking
sits at the centre of a range where the 13 queries of search_gate.py
all answer, in the search box itself.

839 pages, every URL and 45,611 ids match the MkDocs build. The tests
read the Starlight content and syntax.

wiki/technical-faq.md

@@ -143,7 +143,8 @@ Running `verify.py --emulator <core> --verbose` shows the emulator-level ground
 
 It reaches only as far as the profiles do. Files no profile states a value for are platform-only, and nothing can be said about their content. The footer of the platform report gives that ratio as `Ground truth: N/M files have emulator validation`.
 
-!!! tip "Next"
+:::tip[Next]
+- [Reference index](index.md), every reference page in one list
+- For contributors: [How to contribute](../contributing.md)
+:::
 
-    - [Reference index](index.md), every reference page in one list
-    - For contributors: [How to contribute](../contributing.md)