feat(mcp): expose ai_summary in dbn_get_document response

LEFT JOIN doc_summaries so the document object includes ai_summary
and summary_model alongside id/title. Returns null for docs not yet
backfilled.

api/document-chunks.php

@@ -18,7 +18,13 @@ try {
 
     $ragDb = dbnToolsRagDb();
 
-    $docStmt = $ragDb->prepare("SELECT id, title FROM documents WHERE id = ? LIMIT 1");
+    $docStmt = $ragDb->prepare("
+        SELECT d.id, d.title, ds.summary AS ai_summary, ds.summary_model
+        FROM documents d
+        LEFT JOIN doc_summaries ds ON ds.document_id = d.id
+        WHERE d.id = ?
+        LIMIT 1
+    ");
     $docStmt->execute([$documentId]);
     $doc = $docStmt->fetch(PDO::FETCH_ASSOC);
     if (!$doc) {
@@ -44,7 +50,12 @@ try {
 
     echo json_encode([
         'ok'       => true,
-        'document' => ['id' => (int)$doc['id'], 'title' => (string)$doc['title']],
+        'document' => [
+            'id'            => (int)$doc['id'],
+            'title'         => (string)$doc['title'],
+            'ai_summary'    => $doc['ai_summary'] ?? null,
+            'summary_model' => $doc['summary_model'] ?? null,
+        ],
         'chunks'   => $chunks,
     ], JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);