feat(arap): record an invoice's sends as invoice.sent (P4b S5)

The books never send invoices (A-4), but they must remember that one
went out: who sent it, how, to whom, when, whether it was the original
or a reminder, and the channel's own reference. That record is a fact
of the document's life, not a figure: a send moves no money, so it is
one journal line (`invoice.sent`) and no entry, and every derived
figure (outstanding, aging, DocState) is exactly as it was.

`Ledger::mark_sent` refuses a send on a void invoice (it should never
have reached the customer), a send dated before the invoice, no
recipients, and any recipient, reference or note that would put a full
TIN or control characters into the journal. Open, partial, paid and
written-off invoices can be sent (a copy for the customer's records, a
reminder).

The event is `documents_v2`'s (D-52): an older version refuses the
type rather than dropping the record. Replay restores it and the
projection keeps it in schema 16's `invoice_sends` table, so live,
replay and the viewer agree. The new old-books fixture `p4_s5_before`
was written by eeee9658 and opens to the same figures; a hand-written
send in `books_written_under_older_rules_still_open` proves an older
journal with the new line still opens.

Tests: mark_sent_waits_for_documents_v2, sends_replay_and_project,
a_send_changes_no_figure, mark_sent_on_void_refused, Op::MarkSent in
status_is_a_function_of_journal_and_date,
an_older_version_stops_at_invoice_sent.

crates/ledger-store/tests/fixtures/old-books-writer/src/bin/s5_before.rs

@@ -0,0 +1,65 @@
+//! Writes `p4_s5_before`: books the version before P4b S5 (main eeee9658)
+//! wrote through its Store API: a chart, a customer's invoice part paid,
+//! and a vendor's bill. No send exists in that version; this version opens
+//! the same journal and must report the same figures.
+use chrono::NaiveDate;
+use ledger_core::{AccountType, Currency, DocRef, DocumentLine, Money, Side};
+use ledger_store::Store;
+use rust_decimal::Decimal;
+use std::path::PathBuf;
+
+fn d(y: i32, m: u32, day: u32) -> NaiveDate {
+    NaiveDate::from_ymd_opt(y, m, day).unwrap()
+}
+fn cents(c: i64) -> Decimal {
+    Decimal::new(c, 2)
+}
+fn line(what: &str, c: i64) -> DocumentLine {
+    DocumentLine {
+        description: what.into(),
+        amount: cents(c),
+        class_id: None,
+        account: None,
+        quantity: None,
+        unit_price: None,
+    }
+}
+
+fn main() {
+    let root = PathBuf::from(std::env::args().nth(1).unwrap());
+    let dir = root.join("p4_s5_before");
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let mut s = Store::create(&dir, Currency::USD).unwrap();
+    let bank = s
+        .add_account("1000", "Bank", AccountType::Asset, None, false)
+        .unwrap();
+    let capital = s
+        .add_account("3000", "Capital", AccountType::Equity, None, false)
+        .unwrap();
+    let seed = s.create_entry(d(2026, 1, 1), "Opening capital").unwrap();
+    let m = Money::new(Decimal::from(1000), Currency::USD);
+    s.add_line(seed, bank, Side::Debit, m).unwrap();
+    s.add_line(seed, capital, Side::Credit, m).unwrap();
+    s.post_entry(seed).unwrap();
+    let fernhill = s.add_customer("Fernhill Labs").unwrap();
+    let vendor = s.add_vendor("Tobin Harlow Supply").unwrap();
+    let inv = s
+        .create_invoice(
+            fernhill,
+            d(2026, 2, 1),
+            d(2026, 3, 3),
+            vec![line("Design", 120_000)],
+        )
+        .unwrap();
+    s.receive_payment(inv, d(2026, 2, 15), cents(40_000), bank)
+        .unwrap();
+    s.create_bill(
+        vendor,
+        d(2026, 2, 10),
+        d(2026, 3, 12),
+        vec![line("Drafting", 30_000)],
+    )
+    .unwrap();
+    println!("WROTE {:?} (invoice {inv}, {:?})", dir, DocRef::Invoice(inv));
+}