feat: show document title and link in competitive signals panel

Replace raw UUID with a linked document title in both the collapsed
row (using the empty space on the right) and the expanded detail view.
Uses useDocument hook to fetch the title, falls back to truncated UUID
while loading. Clicking the link navigates to the document detail page.

frontend/src/pages/CompanyDetail.tsx

@@ -1,4 +1,4 @@
-import { useParams, useNavigate } from '@tanstack/react-router';
+import { useParams, useNavigate, Link } from '@tanstack/react-router';
 import { useState } from 'react';
 import {
   useCompany,
@@ -14,6 +14,7 @@ import {
   useTrends,
   useTrendHistory,
   useMarketPrices,
+  useDocument,
 } from '../api/hooks';
 import { StatusBadge, ConfidenceBar, LoadingSpinner, Card } from '../components/ui';
 import { DataTable, type Column } from '../components/DataTable';
@@ -444,10 +445,23 @@ function CompetitiveSignalsPanel({ signals }: { signals: CompetitiveSignal[] })
       ) : (
         <div className="space-y-2">
           {signals.map((s) => (
-            <div key={s.id}>
+            <SignalRow key={s.id} signal={s} expanded={expandedId === s.id} onToggle={() => setExpandedId(expandedId === s.id ? null : s.id)} />
+          ))}
+        </div>
+      )}
+    </div>
+  );
+}
+
+function SignalRow({ signal: s, expanded, onToggle }: { signal: CompetitiveSignal; expanded: boolean; onToggle: () => void }) {
+  const { data: doc } = useDocument(s.source_document_id);
+  const docLabel = doc?.title ?? `doc:${s.source_document_id.slice(0, 8)}…`;
+
+  return (
+    <div>
       <div
         className="flex items-center justify-between rounded-lg border border-cyan-700/30 bg-cyan-900/10 p-3 cursor-pointer hover:border-cyan-500/50"
-                onClick={() => setExpandedId(expandedId === s.id ? null : s.id)}
+        onClick={onToggle}
       >
         <div className="flex items-center gap-3">
           <span className="rounded bg-cyan-900/40 border border-cyan-700/50 px-1.5 py-0.5 text-[10px] font-medium text-cyan-400">COMPETITIVE</span>
@@ -457,11 +471,20 @@ function CompetitiveSignalsPanel({ signals }: { signals: CompetitiveSignal[] })
           <StatusBadge status={s.signal_direction} />
         </div>
         <div className="flex items-center gap-3">
+          <Link
+            to="/documents/$id"
+            params={{ id: s.source_document_id }}
+            className="max-w-[180px] truncate text-xs text-brand-400 hover:underline"
+            onClick={(e) => e.stopPropagation()}
+            title={doc?.title ?? s.source_document_id}
+          >
+            {docLabel}
+          </Link>
           <ConfidenceBar value={s.signal_strength} />
           <span className="text-xs text-gray-500">{new Date(s.computed_at).toLocaleDateString()}</span>
         </div>
       </div>
-              {expandedId === s.id && (
+      {expanded && (
         <Card className="mt-1 ml-4">
           <dl className="grid grid-cols-2 gap-x-6 gap-y-2 text-xs sm:grid-cols-3">
             <div>
@@ -490,7 +513,16 @@ function CompetitiveSignalsPanel({ signals }: { signals: CompetitiveSignal[] })
             </div>
             <div>
               <dt className="text-gray-500">Source Document</dt>
-                      <dd className="font-mono text-gray-400 text-[10px]">{s.source_document_id}</dd>
+              <dd>
+                <Link
+                  to="/documents/$id"
+                  params={{ id: s.source_document_id }}
+                  className="text-brand-400 hover:underline"
+                  onClick={(e) => e.stopPropagation()}
+                >
+                  {docLabel}
+                </Link>
+              </dd>
             </div>
             <div>
               <dt className="text-gray-500">Computed At</dt>
@@ -500,10 +532,6 @@ function CompetitiveSignalsPanel({ signals }: { signals: CompetitiveSignal[] })
         </Card>
       )}
     </div>
-          ))}
-        </div>
-      )}
-    </div>
   );
 }