`+append --json-values` flattens multi-row arrays into a single row

[ncoop57]

Description

When using +append --json-values with a multi-row JSON array, all values are appended as a single row instead of separate rows.

Steps to Reproduce

# Append 2 rows via --json-values
gws sheets +append --spreadsheet <ID> --json-values '[["Alice","100"],["Bob","200"]]'

Expected: 2 rows appended

A	B
Alice	100
Bob	200

Actual: 1 row appended with all values concatenated across columns

A	B	C	D
Alice	100	Bob	200

Possible Cause

This may be related to parse_append_args in src/helpers/sheets.rs — the --json-values branch parses the input as Vec<Vec<String>> but then calls .flatten().collect(), collapsing it into a single flat Vec<String>. Is this intentional, perhaps to support a specific use case? If not, it looks like AppendConfig.values would need to become Vec<Vec<String>> to preserve the row structure through to build_append_request.

Workaround

Using the raw API works correctly for multi-row appends:

gws sheets spreadsheets values append \
  --params '{"spreadsheetId": "<ID>", "range": "Sheet1!A1", "valueInputOption": "USER_ENTERED"}' \
  --json '{"values": [["Alice","100"],["Bob","200"]]}'