feat(pdf): the issued invoice carries what the customer pays from (P4b S4.5)

The page a customer pays from must show what the books issued, and only
that. InvoiceDoc gains each line's quantity and unit price ("3 x $33.33"
beside the line's own amount, never recomputed), the customer's PO, memo,
footer, the ways to pay (a QR code through labels::qr_svg for a method
with a link that asks for one), the seller's email and website, and a
Ship-to block. InvoiceVersion separates the issued copy (no stamp, no
settled rows, no "re-created" note) from the current copy, whose
"Re-created on" note prints the as_of it was given, never the wall clock,
so the bytes stay deterministic (B-40 item 3). Every amount reaches the
page through report::amount_parts; every string is data.

ledger_package builds all three copies (issued, DRAFT, current) from one
function over the invoice's own snapshots (A-13, D-55: number, terms,
bill-to contact block, shipping address), falling back to the party record
only for a document made before snapshots, so the three cannot disagree.
invoice_document drops its now-unused `today` argument.

rules.md gains B-39 (terms) and B-40 (numbers and the issued copy) from
the 8.3.13 spec blocks, CONVENTION until their sources are vendored.
No golden moved: the render test never held a hash, it compares two
renders for equal bytes, and still does.

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

crates/ledger-gui/src/pages/invoices.rs

@@ -658,7 +658,6 @@ fn pdf_actions(ui: &mut Ui, b: &Books, id: ledger_core::InvoiceId) {
                 &b.settings.company,
                 id,
                 b.today,
-                b.today,
             )
             .and_then(|doc| {
                 ledger_import::invoice_pdf::invoice_pdf(&doc).map_err(|e| e.to_string())