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/modal.js

@@ -181,13 +181,17 @@
     // is open (e.g. the merge step replacing the move dialog); focus returns
     // to where it was before the first one opened.
     var hostPrevFocus = null;
+    // History restores swap without event details; they never target the host.
+    function isHost(e) {
+        return !!(e.detail && e.detail.target && e.detail.target.id === 'modal-host');
+    }
     document.addEventListener('htmx:beforeSwap', function (e) {
-        if (e.detail.target.id !== 'modal-host') return;
+        if (!isHost(e)) return;
         hostPrevFocus = current ? detach(true) : document.activeElement;
     });
     document.addEventListener('htmx:afterSwap', function (e) {
+        if (!isHost(e)) return;
         var host = e.detail.target;
-        if (host.id !== 'modal-host') return;
         var backdrop = host.querySelector('.modal-backdrop');
         if (!backdrop) return;
         show(backdrop, host, hostPrevFocus);