Fix MariaDB LIMIT/OFFSET bound-parameter error in corpus API

MariaDB rejects ? placeholders for LIMIT/OFFSET when emulate_prepares=false.
Interpolate $limit and $offset as ints directly into SQL strings in both
corpus-documents.php and corpus-search.php BM25 paths.

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

api/corpus-documents.php

@@ -53,11 +53,8 @@ try {
     $countStmt->execute($countParams);
     $total = (int)$countStmt->fetchColumn();
 
-    // Paginated rows
-    $dataParams   = $params;
-    $dataParams[] = $limit;
-    $dataParams[] = $offset;
-    $dataStmt     = $ragDb->prepare(
+    // Paginated rows — LIMIT/OFFSET interpolated as ints (MariaDB rejects bound params here)
+    $dataStmt = $ragDb->prepare(
         "SELECT d.id, d.title, d.category, d.source_url, d.language, d.updated_at,
                 COUNT(c.id) AS chunk_count
          FROM documents d
@@ -65,9 +62,9 @@ try {
          WHERE $whereStr
          GROUP BY d.id
          ORDER BY d.updated_at DESC
-         LIMIT ? OFFSET ?"
+         LIMIT $limit OFFSET $offset"
     );
-    $dataStmt->execute($dataParams);
+    $dataStmt->execute($params);
     $documents = $dataStmt->fetchAll(PDO::FETCH_ASSOC);
 
     // Normalise chunk_count to int