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

crates/ledger-cli/tests/spec_mcp.rs

@@ -906,6 +906,13 @@ fn happy_path(name: &str) -> Mcp {
         json!({"kind": "invoices", "status": "all"}),
     );
     m.ok("books.document", json!({"ref": format!("invoice:{inv}")}));
+    // P4b S5: the invoice went out (the books record the send, never make it).
+    m.ok(
+        "books.mark_sent",
+        json!({"invoice": format!("invoice:{inv}"), "on": "2026-02-03",
+               "by": "Avery Quill", "recipients": ["billing@client.example"],
+               "reference": "msg-1"}),
+    );
 
     // Fixed assets.
     let registered = m.ok(