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-mcp/src/tools/documents.rs

@@ -1038,13 +1038,8 @@ impl BooksServer {
             }
             (true, ledger_core::DocRef::Invoice(id)) => {
                 let settings = self.settings();
-                let printed = ledger_package::invoice_document(
-                    ledger,
-                    &settings.company,
-                    id,
-                    as_of,
-                    today(),
-                )?;
+                let printed =
+                    ledger_package::invoice_document(ledger, &settings.company, id, as_of)?;
                 let bytes =
                     ledger_import::invoice_pdf::invoice_pdf(&printed).map_err(|e| e.to_string())?;
                 Some(self.hand_over(