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

plan/STATUS.md

@@ -161,3 +161,12 @@ interface is MCP, not a cloned GUI. The first storage + MCP slice is done
   closes a silent path for moving a receipt off a posted entry; disposals
   check their receipt ids before posting. Schema v5. First real use: swapping
   the migrated Wanderland Labs `.eml` receipts for their PDF renders.
+- 2026-10-11: The cash flow statement is a first-class output everywhere the
+  other two statements are: `cash_flow_pdf` in ledger-import, a `pdf`
+  format on `books.export` (P&L, balance sheet, cash flow), and
+  `cash-flow.pdf` in the CPA package, which now requires `cash_accounts`
+  (the statement reconciles to them). Known gaps, next: the P&L and balance
+  sheet PDF/XLSX ignore start/end/as_of (all-time balances under the
+  requested label; core needs period-scoped statements); P&L and balance
+  sheet XLSX are totals-only; PDF amounts don't align (padding in a
+  proportional font), no company name, negatives as "-x".