merge: P4b S5, sent tracking (branch S5, ad649be3)

The second of the paused branches. invoice.sent, Ledger::mark_sent (with
its Lean step), books.mark_sent in its own group, the two attention
items, schema 17. Conflicts, resolved as plan 8.0.2 says: the shared
over-the-wire test file crates/ledger-cli/tests/documents.rs (S4.4's
file kept whole, S5's test appended, its create call given the
confirmed: true the S4.4 contract now needs), types.rs (both appends
kept), docs/parity.md (the review's oracle row and S5's new row).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

docs/architecture.md

@@ -169,6 +169,7 @@ groups are:
 
 - `documents` — invoices, bills, payments, voids, `books.documents`,
   `books.document`, the control check and the agings;
+- `sent` — `books.mark_sent`, the record that an invoice went out (P4b S5);
 - `entries` — `books.draft_entry`, `books.add_line`, `books.post_entry`,
   `books.reverse_entry`, `books.get_entry`, `books.search_entries`, the
   bank CSV import;