feat: search works in static exports (0.1.15-alpha)

[Shewart]

Summary

Search was the last piece of chrome that needed a running Blazor app, so a shelldocs build export had none. Search now runs in the browser, the same way on a running app and on a static host.

What changed

• The app serves its search index at /_shelldocs/search.json (title, description, section, body and owning version per entry). It is added by a startup filter, like the redirect map, so sites need no Program.cs change. Responses carry an ETag and revalidate.
• shelldocs.js does the searching. SearchDialog is now a hidden template with no Blazor handlers. On Cmd/Ctrl+K or a [data-search-open] button, the script clones it onto <body>, fetches the index once and ranks it with the same scoring as before (title, section, description, body, with body snippets), scoped to the current version. Results are links.
• shelldocs build copies the index to _shelldocs/search.json in the export, and warns when the site's ShellDocs.Components is too old to serve one.
• Works under --base-href: the index and result links resolve against <base>.

Behaviour changes

• Search buttons are [data-search-open] buttons; add the attribute to any element to open search from it. shelldocsSearch.open() still works from script, and there is a shelldocsSearch.close().
• SearchState is no longer used and is kept only so existing code compiles. shelldocsSearch.init is gone.

Commits

• feat(components): serve the search index at /_shelldocs/search.json
• feat(search): search in the browser, without a Blazor runtime
• feat(cli): copy the search index into the static export
• docs: search works in static exports
• chore: bump to 0.1.15-alpha, changelog

Each commit builds with 0 warnings and passes its tests on its own (347 / 350 / 351 / 351 / 351).

Testing

• Release build: 0 warnings. 351 tests pass, 8 of them new (StaticSearchTests).
• Example site in the browser, three ways: running app, shelldocs build export served by python -m http.server, and the export under a /sub/ base href. In each: Cmd/Ctrl+K, search button, typing, arrow keys, Enter, Escape, backdrop click, and version scoping on unversioned and versioned pages.
• Keystrokes were sent by script. The dialog has not been checked by eye or at phone width.
• Pack produces the six 0.1.15-alpha packages.