feat(dashboard): extend shift+click suggestions to sidebar navigation

- Click handler: sidebar <a> and <summary> are no longer excluded;
  e.preventDefault() stops navigation while shift is held
- _inferWidgetName: sidebar-first branch returns nav link text,
  section heading text, or "Navigation" fallback
- pageName is "Navigation" for sidebar clicks (not the current page title)
- CSS: sidebar a and summary highlighted (dashed indigo outline + tint)
  when shift is held, same as main content widgets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/src/components/improvement-modal.js

@@ -149,7 +149,9 @@ function _ensureStyles() {
 .impr-mode-shift #observablehq-main h2,
 .impr-mode-shift #observablehq-main h3,
 .impr-mode-shift #observablehq-main h4,
-.impr-mode-shift #observablehq-main [data-widget-name] {
+.impr-mode-shift #observablehq-main [data-widget-name],
+.impr-mode-shift #observablehq-sidebar a,
+.impr-mode-shift #observablehq-sidebar summary {
   outline: 1px dashed rgba(99, 102, 241, 0.45);
   background: rgba(99, 102, 241, 0.055) !important;
   border-radius: 4px;
@@ -161,6 +163,15 @@ function _ensureStyles() {
 
 /* ── Widget name inference ─────────────────────────────────────────────── */
 function _inferWidgetName(target) {
+  // 0. Sidebar navigation: nav link text or section heading
+  if (target.closest("#observablehq-sidebar")) {
+    const link    = target.closest("a");
+    if (link)    return link.textContent.trim() || "Nav link";
+    const summary = target.closest("summary");
+    if (summary) return summary.textContent.trim() || "Nav section";
+    return target.textContent.trim() || "Navigation";
+  }
+
   // 1. Explicit data-widget-name on self or ancestor
   let el = target;
   while (el && el !== document.body) {
@@ -238,15 +249,19 @@ export function initImprovementModal({ apiBase = "http://127.0.0.1:8000", domain
 
   document.addEventListener("click", (e) => {
     if (!e.shiftKey) return;
-    // Don't intercept shift-clicks on form controls or links
-    if (e.target.matches("input, textarea, select, a, button")) return;
+    const inSidebar = !!e.target.closest("#observablehq-sidebar");
+    // Block shift-clicks on form controls; allow sidebar links (preventDefault stops navigation)
+    if (!inSidebar && e.target.matches("input, textarea, select, a, button")) return;
+    if (inSidebar  && e.target.matches("input, textarea, select")) return;
 
     e.preventDefault();
 
     const widgetName = _inferWidgetName(e.target);
-    const pageName   = document.title
-      ? document.title.replace(" – Custodian State Hub", "").trim()
-      : (location.pathname.replace(/^\//, "") || "Overview");
+    const pageName   = inSidebar
+      ? "Navigation"
+      : (document.title
+          ? document.title.replace(" – Custodian State Hub", "").trim()
+          : (location.pathname.replace(/^\//, "") || "Overview"));
 
     // Remove any open modal
     document.getElementById("_impr-root")?.remove();