fix(brightdata): default mode field to empty so it's opt-in like other advanced params

Greptile flagged that mode shipped with a non-empty default ('standard'),
causing it to be sent on every Discover call unlike the sibling dataFormat
field which uses an empty/None default and only sends when the user opts in.
Aligns mode with that same pattern.

Author: waleedlatif1

apps/sim/blocks/blocks/brightdata.ts

@@ -143,12 +143,12 @@ export const BrightDataBlock: BlockConfig<BrightDataResponse> = {
       title: 'Search Mode',
       type: 'dropdown',
       options: [
-        { label: 'Standard', id: 'standard' },
+        { label: 'Standard (Default)', id: '' },
         { label: 'Deep', id: 'deep' },
         { label: 'Fast', id: 'fast' },
         { label: 'Zero Ranking', id: 'zeroRanking' },
       ],
-      value: () => 'standard',
+      value: () => '',
       mode: 'advanced',
       condition: { field: 'operation', value: 'discover' },
     },