The preview feature serves both accounts and stock vouchers (SI/PI/PE + DN/PR/SE)
and its show_*_preview entry points live in controllers/stock_controller, so the
cohesive GL+SLE preview module belongs in controllers/, not stock/services/. Pure
move + import-path update; GL and stock previews stay together (shared get_columns/
get_data formatters; read-side, kept out of the write-path services).
Verified: ledger snapshots green; module resolves at new path.
c5ff1009b2