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/companion.js

@@ -200,13 +200,20 @@
         // leaves the status icon and reveal buttons invisible on mobile.
         if (isMobileDevice()) return;
         probeStatus().then(function () {
-            updateFooterIcon();
-            wireFileLinks();
-            wireRevealButton();
-            wireFileRevealButtons();
+            wireFileLinks(); // delegated to document: once
+            applyToPage();
+            // Boosted navigation swaps in a new page without reloading this
+            // script: re-apply to its footer icon and reveal buttons.
+            document.addEventListener('page:swapped', applyToPage);
         });
     }
 
+    function applyToPage() {
+        updateFooterIcon();
+        wireRevealButton();
+        wireFileRevealButtons();
+    }
+
     if (document.readyState === 'loading') {
         document.addEventListener('DOMContentLoaded', init);
     } else {