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/hostile_args.rs

@@ -1017,13 +1017,13 @@ fn inputs_that_once_panicked_are_refused_or_answered() {
         ),
         (
             "books.create_invoice",
-            json!({"party_id": client, "date": "2026-05-01", "due_date": "2026-06-01",
+            json!({"customer": (client).to_string(), "date": "2026-05-01", "due_date": "2026-06-01",
                    "lines": [{"description": "a", "amount": MAX},
                              {"description": "b", "amount": "1"}], "confirmed": true}),
         ),
         (
             "books.create_bill",
-            json!({"party_id": acme, "date": "2026-05-01", "due_date": "2026-06-01",
+            json!({"vendor": (acme).to_string(), "date": "2026-05-01", "due_date": "2026-06-01",
                    "vendor_ref": "H-1",
                    "lines": [{"description": "a", "amount": MAX, "account": "6000"},
                              {"description": "b", "amount": "1", "account": "6000"}],
@@ -1031,7 +1031,7 @@ fn inputs_that_once_panicked_are_refused_or_answered() {
         ),
         (
             "books.create_invoice",
-            json!({"party_id": client, "date": "2026-05-01", "due_date": "+262142-12-31",
+            json!({"customer": (client).to_string(), "date": "2026-05-01", "due_date": "+262142-12-31",
                    "lines": [{"description": "a", "amount": "1"}], "confirmed": true}),
         ),
         (