feat: real dates and per-account detail in every statement export

Every statement export rendered life-of-ledger totals under whatever date
range or as-of label was asked for, and the P&L and balance sheet XLSX
were totals-only. Now:

- books.profit_and_loss / books.balance_sheet and the csv, json, xlsx,
  pdf exports and CPA package all use core's profit_and_loss_for_period
  and balance_sheet_as_of, with a line per account. The tools keep their
  totals and add revenue/expense/asset/liability/equity account lines.
  An omitted start is the first posted entry, never "0001-01-01".
- ledger-import::report lays a statement out once (section, line,
  subtotal, total) for every renderer, with one exact amount formatter:
  thousands separators, negatives in parentheses, no floats. XLSX keeps
  numeric cells with an accounting number format, named sheets, company
  header, totals with borders; the trial balance gains its totals row.
- ledger-mcp reads wanderbooks.toml (next to --data-dir, or
  --books-toml): company name for headers, fiscal_year_start for the CPA
  package's fiscal year to date (end derived; Feb 29 rejected), and
  [books] receipt_threshold, which the server had been ignoring.
  config.json's receipt_policy still wins when set. New dependency: toml
  1.x (already in the lockfile via another crate).
- Store::journal_seq(); every report notes the journal seq it reflects.

Tests: company.rs unit tests (fiscal years incl. a July start, scaffold
parsing, bad settings); report.rs formatting tests; an MCP stdio test with
--books-toml (threshold 5.00 enforced, February-only P&L with account
lines, start defaults to the first entry, as-of balance sheet).

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

crates/ledger-store/src/store.rs

@@ -1981,6 +1981,12 @@ impl Store {
     // Maintenance: verify and rebuild
     // ------------------------------------------------------------------
 
+    /// Sequence number of the last journal line: the exact journal state a
+    /// report reflects. Zero for an empty journal.
+    pub fn journal_seq(&self) -> u64 {
+        self.journal.next_seq() - 1
+    }
+
     /// Verify everything: the journal hash chain, a fresh replay's reports
     /// against the live ledger, and the SQLite projection against the replay.
     /// Loud on any divergence.