refactor(mcp): the party_id, document_id and cash_account aliases are removed (P5)

Agent reason: one name for one thing. S4 and S6 kept the old spellings "until
P5" so an agent that learned them did not break; P5 removes them, so the
schema an agent reads has one parameter for each fact and a call cannot name
the same thing twice with different answers.

books.create_invoice takes customer and books.create_bill vendor (a record's
id, its party's id or its name; required), no party_id.
books.receive_payment and books.pay_bill take invoice or bill and
deposit_to or paid_from, no document_id or cash_account; a payment names its
document and its account or is refused saying which to pass. A number that is
one record's id and another's name is still refused, never guessed (INVARIANT
6).

The over-the-wire tests that used the old spellings now use the new
(document_id becomes invoice or bill, cash_account becomes deposit_to or
paid_from, party_id becomes customer or vendor given as the id's text); the
one test that named the alias, party_id_alias_still_works, is now
a_customer_by_id_and_by_name_is_one_record and checks the same two spellings
of a customer, by id and by name, name one record.

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

crates/ledger-cli/tests/projects_parity.rs

@@ -274,7 +274,7 @@ fn invoiced_and_billed_project_figures_are_the_same_in_the_viewer_and_from_the_s
     let bill = server.tool("books.create_bill", bill_args);
     server.tool(
         "books.receive_payment",
-        json!({"confirmed": true, "document_id": inv["id"], "date": "2026-02-20", "amount": "1830.00", "cash_account": "1000"}),
+        json!({"confirmed": true, "invoice": inv["id"], "date": "2026-02-20", "amount": "1830.00", "deposit_to": "1000"}),
     );
     let b = data::load_once(&Source {
         data_dir: data.clone(),