feat(nav): partial HTMX navigation — swap main content without full reload

Intercept internal links and load only .main-wrapper via htmx.ajax, keeping the sidebar/header shell in place. Adds history pushState/popstate handling, sidebar active-state resync and document title update. Moves page script blocks inside #main-content so they run on swap, and makes editor/board scripts idempotent. Routes navigateTo/breadcrumb/library/local-workspace through window.fdNavigate and fixes the duplicated navigateTo definition.

app/templates/_notification_bell.html

@@ -73,6 +73,9 @@ document.addEventListener('alpine:init', function () {
         var self = this;
         this._timer = setInterval(function () { self.refreshCount(); }, 30000);
       },
+      destroy() {
+        if (this._timer) { clearInterval(this._timer); this._timer = null; }
+      },
       toggle() { this.open = !this.open; if (this.open) this.load(); },
       timeAgo(s) {
         if (!s) return '';