Financial statements

Financial statements (P&L, balance sheet, cash movement) read from the DuckLake database finance_books at a named commit (AT (VERSION => n)), pinned to snapshot 2. Commit picker from finance.close_log, compare mode shades cells that differ between two commits and lists the ledger rows posted between them (posted_in), and an Explain panel traces any cell to SQL, rows, and GL entries at that commit. Part of 0903-finance-stable-dives.