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-search.php

@@ -59,10 +59,9 @@ try {
                       AND d.source_url NOT LIKE ?
                     $catClause
                     ORDER BY score DESC
-                    LIMIT ?";
+                    LIMIT $limit";
             $params = [$query, 1, $query, $excludeLike];
             if ($category !== null) $params[] = $category;
-            $params[] = $limit;
             $stmt = $ragDb->prepare($sql);
             $stmt->execute($params);
             $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
@@ -80,11 +79,10 @@ try {
                       AND d.source_url NOT LIKE ?
                     $catClause
                     ORDER BY (d.title LIKE ?) DESC
-                    LIMIT ?";
+                    LIMIT $limit";
             $params = [1, $like, $like, $excludeLike];
             if ($category !== null) $params[] = $category;
             $params[] = $like;
-            $params[] = $limit;
             $stmt = $ragDb->prepare($sql);
             $stmt->execute($params);
             $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);