Add AI-suggested editable document title

AI now returns a short descriptive title per document (e.g. "ACME Corp
Invoice April 2026"). Title is stored in a new documents.title column
(migration 0002), shown in the row header instead of the raw filename,
and editable inline via PATCH /documents/{id}/title. Filename is shown
as a subtitle when a title exists.

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

frontend/src/pages/DocumentsPage.tsx

@@ -13,6 +13,7 @@ import {
   assignCategory,
   removeCategory,
   updateDocumentTags,
+  updateDocumentTitle,
   type DocumentOut,
   type CategoryOut,
 } from "../api/client";
@@ -89,6 +90,73 @@ function SuggestionChip({ name, existing, onAccept, onDismiss }: SuggestionChipP
 
 // ── Document row ────────────────────────────────────────────────────────────
 
+// ── Inline title editor ─────────────────────────────────────────────────────
+
+function InlineTitleEditor({
+  docId,
+  currentTitle,
+  filename,
+  onSaved,
+}: {
+  docId: string;
+  currentTitle: string | null;
+  filename: string;
+  onSaved: () => void;
+}) {
+  const [editing, setEditing] = useState(false);
+  const [value, setValue] = useState(currentTitle ?? "");
+
+  const saveMut = useMutation({
+    mutationFn: (t: string) => updateDocumentTitle(docId, t),
+    onSuccess: () => { onSaved(); setEditing(false); },
+  });
+
+  if (!editing) {
+    return (
+      <span style={{ display: "inline-flex", alignItems: "center", gap: 8 }}>
+        <span style={{ fontWeight: 500 }}>
+          {currentTitle ?? <span style={{ color: "#aaa", fontStyle: "italic" }}>{filename}</span>}
+        </span>
+        <button
+          onClick={(e) => { e.stopPropagation(); setValue(currentTitle ?? ""); setEditing(true); }}
+          style={{ fontSize: 11, cursor: "pointer", color: "#888", background: "none", border: "1px solid #ddd", borderRadius: 3, padding: "0 5px" }}
+          title="Edit title"
+        >
+          ✎
+        </button>
+      </span>
+    );
+  }
+
+  return (
+    <span onClick={(e) => e.stopPropagation()} style={{ display: "inline-flex", alignItems: "center", gap: 6, flex: 1 }}>
+      <input
+        value={value}
+        onChange={(e) => setValue(e.target.value)}
+        onKeyDown={(e) => {
+          if (e.key === "Enter") saveMut.mutate(value);
+          if (e.key === "Escape") { setEditing(false); setValue(currentTitle ?? ""); }
+        }}
+        style={{ fontSize: 14, padding: "2px 6px", border: "1px solid #888", borderRadius: 3, width: 280 }}
+        autoFocus
+      />
+      <button
+        onClick={() => saveMut.mutate(value)}
+        disabled={saveMut.isPending}
+        style={{ fontSize: 12, cursor: "pointer", padding: "2px 8px", background: "#222", color: "#fff", border: "none", borderRadius: 3 }}
+      >
+        {saveMut.isPending ? "…" : "Save"}
+      </button>
+      <button
+        onClick={() => { setEditing(false); setValue(currentTitle ?? ""); }}
+        style={{ fontSize: 12, cursor: "pointer", padding: "2px 6px", border: "1px solid #ccc", borderRadius: 3, background: "none" }}
+      >
+        ✕
+      </button>
+    </span>
+  );
+}
+
 // ── Tag editor ──────────────────────────────────────────────────────────────
 
 function TagEditor({
@@ -290,7 +358,19 @@ function DocumentRow({
         style={{ display: "flex", alignItems: "center", gap: 12, padding: "12px 16px", cursor: "pointer" }}
         onClick={() => setExpanded((e) => !e)}
       >
-        <span style={{ flex: 1, fontWeight: 500 }}>{doc.filename}</span>
+        <span style={{ flex: 1 }}>
+          <InlineTitleEditor
+            docId={doc.id}
+            currentTitle={doc.title}
+            filename={doc.filename}
+            onSaved={() => qc.invalidateQueries({ queryKey: ["documents"] })}
+          />
+          {doc.title && (
+            <span style={{ display: "block", fontSize: 11, color: "#999", marginTop: 1 }}>
+              {doc.filename}
+            </span>
+          )}
+        </span>
         <StatusBadge status={doc.status} />
         {doc.document_type && (
           <span style={{ fontSize: 12, color: "#555" }}>{doc.document_type}</span>