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/_page_editor_realtime.html

@@ -37,6 +37,19 @@ window.__fdRT = (function () {
   let emitT = null, selT = null, titleT = null, drawT = null, retryT = null, pollT = null;
   let _pid = 0;
 
+  // Detach global listeners from a previous editor instance so that
+  // partial (HTMX) navigation doesn't accumulate stale handlers.
+  function unbindGlobal() {
+    const g = window.__fdRTGlobal;
+    if (!g) return;
+    try {
+      document.removeEventListener('selectionchange', g.onSel, true);
+      window.removeEventListener('scroll', g.onScroll, true);
+      window.removeEventListener('resize', g.onResize);
+    } catch (e) { /* noop */ }
+    window.__fdRTGlobal = null;
+  }
+
   const clone = (o) => JSON.parse(JSON.stringify(o));
 
   function colorOf(uid) { return COLORS[Math.abs(uid || 0) % COLORS.length]; }
@@ -459,9 +472,14 @@ window.__fdRT = (function () {
     }
     const tEl = document.getElementById('_titleEl');
     if (tEl) tEl.addEventListener('input', titleInput);
-    document.addEventListener('selectionchange', () => { clearTimeout(selT); selT = setTimeout(emitCursor, 150); }, true);
-    window.addEventListener('scroll', scheduleDraw, true);
-    window.addEventListener('resize', scheduleDraw);
+    unbindGlobal();
+    const onSel = () => { clearTimeout(selT); selT = setTimeout(emitCursor, 150); };
+    const onScroll = () => scheduleDraw();
+    const onResize = () => scheduleDraw();
+    document.addEventListener('selectionchange', onSel, true);
+    window.addEventListener('scroll', onScroll, true);
+    window.addEventListener('resize', onResize);
+    window.__fdRTGlobal = { onSel, onScroll, onResize };
   }
 
   function start(ed) {