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>

assets/page/main.html

@@ -1,5 +1,3 @@
-{{define "headScripts"}}<script src="{{asset "page/actions.js"}}"></script>{{end}}
-
 {{define "headerActions"}}{{if .CanEdit}}
 <button class="btn btn-block" onclick="newPage()" title="New page (N)"><span class="btn-icon">{{icon "new"}}</span><span class="btn-label">NEW</span></button>
 <button class="btn btn-block" data-companion-reveal hidden title="Reveal in file manager"><span class="btn-icon">{{icon "reveal"}}</span><span class="btn-label">REVEAL</span></button>