feat(store): draft states and discards are journaled, posted_seq is kept (P4)

Accounting reason: a draft that waits on its receipt, and one thrown
away, are facts about the books' working papers that must survive a
restart and replay identically, or a discarded draft would come back and
hold its period open. entry.draft_state_set and entry.draft_discarded are
drafts_v2's (an older version stops at the declaration instead of
misreading them); no figure moves. Schema 19 (taken at merge as the next
after the current last): entries.posted_seq, and a draft_states table
(drafts are not rows of entries, so the plan's entries.draft_state column
has nowhere to live). posted_seq is the journal line that posted each
entry (entry.posted, entry.reversed, the line that closed a period or
posted a schedule month), identical live and on replay.

8.0.6: a hand-written line of each new shape in
books_written_under_older_rules_still_open; fixture old-books/p4_before
written by 25b52580 (hand entries posted late, a reversal, a document, a
schedule month, a recurring draft, open drafts, a close) opens to the
same figures (serialized entries omit a building state, so no golden
moved); drafts_v2_is_its_own_feature; the fuzzer and GUI journal know the
types.

Tests: draft_states_replay_and_project, drafts_v2_waits_for_the_upgrade,
posted_seq_is_the_posting_lines_seq, an_older_version_stops_at_the_draft_events.

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

crates/ledger-store/tests/fixtures/old-books-writer/Cargo.toml

@@ -11,6 +11,9 @@
 #                                      the revision before P4b S5)
 #   cargo run --bin p2_1099 -- OUT    (p2_vendor_1099: P2's 1099 marks, run
 #                                      against 9c99a0cf, the revision before P3)
+#   cargo run --bin p4_before -- OUT  (p4_before: run against 25b52580, the
+#                                      revision before P4: hand entries posted
+#                                      late, a reversal, open drafts, a close)
 #   cargo run --bin expect -- OUT     (expected.json beside each journal)
 # and copy each journal.jsonl, blobs/ and expected.json into old-books/.
 # x_member_closes was written later, the same way, by main 00226a4c