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>

e2e/playwright.config.js

@@ -1,4 +1,4 @@
-import { defineConfig } from "@playwright/test";
+import { defineConfig, devices } from "@playwright/test";
 
 const port = process.env.E2E_PORT || "8765";
 
@@ -11,11 +11,15 @@ export default defineConfig({
   reporter: "list",
   use: {
     baseURL: `http://127.0.0.1:${port}`,
-    // System Chrome; no Playwright browser download needed.
-    channel: "chrome",
     trace: "retain-on-failure",
     screenshot: "only-on-failure",
   },
+  projects: [
+    // The system Chrome; no browser download needed.
+    { name: "chrome", use: { channel: "chrome" } },
+    // Playwright's Firefox build: npx playwright install firefox
+    { name: "firefox", use: { ...devices["Desktop Firefox"] } },
+  ],
   webServer: {
     command: "node server.mjs",
     url: `http://127.0.0.1:${port}/`,