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/src/schema.rs

@@ -5,7 +5,7 @@
 //! is the current version.
 
 /// Current schema version.
-pub const SCHEMA_VERSION: u32 = 16;
+pub const SCHEMA_VERSION: u32 = 17;
 
 /// Migrations, in order. `MIGRATIONS[i]` migrates from version `i` to `i+1`.
 pub const MIGRATIONS: &[&str] = &[
@@ -417,5 +417,22 @@ ALTER TABLE bills ADD COLUMN received_on TEXT;
 ALTER TABLE bills ADD COLUMN terms TEXT;
 ALTER TABLE bills ADD COLUMN memo TEXT;
 ALTER TABLE bills ADD COLUMN duplicate_reason TEXT;
+"#,
+    r#"
+-- v17: sent tracking (plan P4b S5, `invoice.sent`): one row per recorded
+-- send of an invoice, in the order journaled. A send moves no figure and
+-- no ledger line, so this table is only the projection's copy of the
+-- journal's record (parity with replay). `on` and `by` are quoted: `on`
+-- is an SQL keyword.
+CREATE TABLE IF NOT EXISTS invoice_sends(
+  invoice_id INTEGER NOT NULL,
+  "on" TEXT NOT NULL,
+  "by" TEXT NOT NULL,
+  via TEXT NOT NULL,
+  to_json TEXT NOT NULL,
+  kind TEXT NOT NULL,
+  reference TEXT NULL,
+  note TEXT NULL
+);
 "#,
 ];