feat(store): journal settlements and replay their lines (P4b S6)

Store::settle now journals a settlement once, line for line, and one
payment event per application, so replay rebuilds the same tags and the
projection sees the same entry. A single legacy-shaped payment is still
journaled byte for byte; more than one document, a discount or a fee
needs documents_v2, and a payment accepted only because an earlier one
was reversed still needs document_standing.

Each event names the control line it tags (line) and, when it took one,
its discount and discount line; the fee is on the first application's
event with its line. Replay tags exactly those lines and leaves a line it
cannot match untagged, which books.control_check lists; a legacy event
without line keeps the first-untagged-control-line rule.

Tests: a_settlement_names_its_lines_and_replays (two invoices, a discount
and a fee; event indices match the plan; replay equals live),
settlement_waits_for_documents_v2 (refused with the feature remedy and no
journal line, accepted after the upgrade), and
legacy_payment_events_keep_the_positional_rule. arap_props gains a
Settle op (two documents, discount, fee), and
books_written_under_older_rules_still_open gains a hand-written payment
event of the new shape through JournalWriter (8.0.6 item 1).

crates/ledger-store/tests/arap_props.proptest-regressions

@@ -5,3 +5,4 @@
 # It is recommended to check this file in to source control so that
 # everyone who runs the test benefits from these saved cases.
 cc 704ab49c9bea84359475c3afa56c3354275a353670fc71156fba151f846f4f73 # shrinks to first = [Create(false, 0, 1), Create(false, 0, 1)], then = [Close(1), Hand(false, 1)]
+cc f678814ec34db3abef40116e17e562fe5abe652c09f12600e19841beaf9d6fe6 # shrinks to first = [Create(false, 0, 13902), Settle { a: 0, b: 0, n: 0, cash: 6676, discount: 551, fee: 0 }], then = []