Boost page navigation with htmx

Links and GET forms to wiki pages swap the next page into .shell instead
of loading a new document: the server answers boosted requests and
history restores with a partial (title, page actions out-of-band, shell
content). The header stays, browsers without cross-document view
transitions (Firefox) no longer flash between pages, and the swap runs
as a same-document view transition. Files, the editor, internal
endpoints and POST forms still navigate normally.

Back/Forward refetch pages (no snapshots that could predate a move or
delete); the tree rail keeps its scroll position and the content column
returns to where it was. Mutation redirects swap their result in the
same way. Page scripts that assumed a fresh document now also run after
a swap (toc, contents, companion, scroll-sync, search actions) or
register once (fitness).

The e2e suite now also runs in Firefox.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

search.go

@@ -137,7 +137,7 @@ func (h *handler) handleSearch(w http.ResponseWriter, r *http.Request) {
 	}
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	data.renderTimer = renderTimer{requestStart(r)}
-	if err := searchTmpl.ExecuteTemplate(w, "layout", data); err != nil {
+	if err := searchTmpl.ExecuteTemplate(w, layoutTemplate(w, r, false), data); err != nil {
 		log.Printf("search template error: %v", err)
 	}
 }