feat: cash flow statement PDF, pdf export format, cash flow in CPA package

The cash flow statement was computed and exportable as csv/json/xlsx but
missing from every PDF path, so the CPA package carried two of the three
financial statements. Now:

- ledger-import: cash_flow_pdf renders the indirect-method statement
  (operating with net income, depreciation add-back, working-capital
  lines; investing; financing; net change reconciled to beginning and
  ending cash) from the computed CashFlowStatement, so the period and
  cash accounts are the caller's.
- books.export gains format "pdf" for profit_and_loss, balance_sheet, and
  cash_flow (base64, like xlsx), plus financing_accounts for cash_flow.
- books.export_cpa_package adds cash-flow.pdf (fiscal year to date, like
  the P&L) and requires cash_accounts: without them the statement has
  nothing to reconcile to.
- One cash_flow_statement helper resolves codes and dates for xlsx, pdf,
  and the package.

Test: MCP stdio test exports all three statement PDFs, checks the
cash_accounts and bad-report refusals, and unzips the CPA package to find
all five files. Known report gaps are logged in plan/STATUS.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

crates/ledger-import/src/lib.rs

@@ -17,5 +17,5 @@ pub mod xlsx;
 pub use bank_csv::{BankTransaction, parse_bank_csv};
 pub use chart_csv::{ChartRow, parse_chart_csv};
 pub use iif::{IifEntry, journal_to_iif};
-pub use pdf::{PdfError, balance_sheet_pdf, profit_and_loss_pdf};
+pub use pdf::{PdfError, balance_sheet_pdf, cash_flow_pdf, profit_and_loss_pdf};
 pub use xlsx::{XlsxReport, report_to_xlsx};