Resolves #8551

Changes:
saveTable() only quoted CSV fields containing commas, but never escaped " inside them, producing malformed output. Added csvEscape() next to the existing escapeHelper, which doubles inner quotes and triggers quoting on " and \n too, not just ,. Also fixes headers, which were never quoted at all. Updated the CSV download test to assert against the actual expected RFC 4180 output instead of rebuilding the same broken string.