Google Sheets export action: choose which tab to export when format is CSV

Current behaviour
The “Convert … to CSV” export action offers “CSV (first sheet only)”. For workbooks with several tabs, only the first tab can be exported.

Proposal
When the export format is CSV, add an optional field to select the sheet/tab:

• by tab name or sheet ID (gid), accepting a dynamic value from the flow,

• defaulting to the first sheet, so existing flows keep working.

Nice to have: an “all sheets” option that returns one CSV per tab, with the tab name in the file name.

Why
CSV is the practical format for passing tabular data to AI models. For example, the Gemini API accepts text/csv as a document input, but not Google Sheets or xlsx as a native file. Workbooks with several tabs (data, parameters, lookup tables) currently need a workaround, such as reading ranges with separate actions and rebuilding the CSV, or restructuring the workbook.