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/format_upgrade.rs

@@ -767,7 +767,7 @@ fn books_p2_served_cut_over_whole() {
     let invoice = a
         .call(
             "books.create_invoice",
-            json!({"party_id": 1, "date": "2026-01-05", "due_date": "2026-02-04",
+            json!({"customer": (1).to_string(), "date": "2026-01-05", "due_date": "2026-02-04",
                    "lines": [{"description": "Design", "amount": "400.00"}], "confirmed": true}),
         )
         .unwrap()["id"]
@@ -789,7 +789,7 @@ fn books_p2_served_cut_over_whole() {
     let unpaid = a
         .call(
             "books.create_invoice",
-            json!({"party_id": customer, "date": "2026-01-10", "due_date": "2026-02-09",
+            json!({"customer": (customer).to_string(), "date": "2026-01-10", "due_date": "2026-02-09",
                    "lines": [{"description": "Survey", "amount": "300.00"}], "confirmed": true}),
         )
         .unwrap()["id"]