fix: guard mock suggestions for vectorsdb, optimize fold scan

- Add !isVectorsDb guard to useMockSuggestions derivation
- Use single sliceString for bracket matching instead of per-char rope traversal

src/routes/(console)/project-[region]-[project]/databases/database-[database]/collection-[collection]/(components)/editor/view.svelte

@@ -1039,15 +1039,15 @@
             if (!match) continue;
 
             const bracketPos = line.from + match[1].length;
+            const tail = doc.sliceString(bracketPos, doc.length);
             let depth = 0;
             let closePos = -1;
-            for (let i = bracketPos; i < doc.length; i++) {
-                const ch = doc.sliceString(i, i + 1);
-                if (ch === '[') depth++;
-                else if (ch === ']') {
+            for (let i = 0; i < tail.length; i++) {
+                if (tail[i] === '[') depth++;
+                else if (tail[i] === ']') {
                     depth--;
                     if (depth === 0) {
-                        closePos = i;
+                        closePos = bracketPos + i;
                         break;
                     }
                 }

src/routes/(console)/project-[region]-[project]/databases/database-[database]/collection-[collection]/spreadsheet.svelte

@@ -571,6 +571,7 @@
     const MIN_DOCS_FOR_FUZZY_SUGGESTIONS = 5;
 
     $: useMockSuggestions =
+        !isVectorsDb &&
         $noSqlDocument.isNew &&
         ($documents?.documents?.length ?? 0) < MIN_DOCS_FOR_FUZZY_SUGGESTIONS;