feat: the invoice PDF, with stamps and each payment (P4b S3)

ledger-import invoice_pdf (templates/invoice.typ): seller, bill-to,
number, dates, terms, lines, total, each settled line and the balance
due; money formatted in Rust (the template does no arithmetic), text as
data, deterministic bytes. Stamps as a rubber stamp would mark it, in
red: PAID (with the day it was paid in full: the invoice is then the
customer's receipt), PARTIALLY PAID, PAST DUE, VOID; DRAFT in gray for
S4's preview. ledger-package invoice_document builds it from the books
as of a day: the derived figures (B-38), each payment that stands on its
own line with its date, payment method and reference; re-created copies
say so (the issued copy is kept from S4 on and never changes).
books.document pdf hands it over as a download; the viewer's invoice
page saves or opens it. The owner asked for the paid stamp with the
payment's date and details (2026-10-24).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-package/src/lib.rs

@@ -25,6 +25,7 @@
 
 mod books;
 mod iif;
+mod invoice;
 mod k1_tax;
 mod package;
 mod reports;
@@ -34,6 +35,7 @@ mod vendor_1099;
 
 pub use books::PackageBooks;
 pub use iif::export_iif;
+pub use invoice::invoice_document;
 pub use k1_tax::{open_text, tax_basis_csv};
 pub use package::{Package, PackageRequest, build_package, package_file_name};
 pub use reports::{