fix(ui): say when a part has no datasheet instead of showing an empty tab

91 of the 156 catalogue parts have neither an authored doc nor a metadata
description, so the Datasheet tab rendered nothing but tag chips and read as
broken. It now states plainly that no datasheet is written yet, and points at
the pin map, which IS the useful content for those parts. The picker hover
card gets the same line, since both render one body.

frontend/src/components/ComponentInfoPanel.css

@@ -333,3 +333,10 @@
   flex-shrink: 0;
 }
 
+
+/* No authored doc and no metadata description — most of the catalogue. Say it
+   plainly instead of leaving the panel looking broken. */
+.cip-desc--empty {
+  color: #7a7a7a;
+  font-style: italic;
+}

frontend/src/components/ComponentInfoPanel.tsx

@@ -123,13 +123,20 @@ export const ComponentInfoBody: React.FC<{
 
   return (
     <>
-      {/* Authored datasheet supersedes the thin auto-generated description. */}
+      {/* Authored datasheet supersedes the thin auto-generated description.
+          91 of the 156 catalogue parts have NEITHER, so say so rather than
+          leaving the reader looking at an empty panel wondering if it broke. */}
       {doc?.body ? (
         <div className="cip-doc">
           <ReactMarkdown remarkPlugins={[remarkGfm]}>{doc.body}</ReactMarkdown>
         </div>
+      ) : data.description ? (
+        <p className="cip-desc">{data.description}</p>
       ) : (
-        data.description && <p className="cip-desc">{data.description}</p>
+        <p className="cip-desc cip-desc--empty">
+          No datasheet written for this part yet.
+          {data.pinCount > 0 && ' Its pins are listed on the left.'}
+        </p>
       )}
 
       {showProps && shownProps.length > 0 && (