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

docs/receipt-store.md

@@ -61,7 +61,11 @@ apply is safe — on startup the applier replays every journal line with
   never a ledger line or a figure; P4b S5), `invoice.written_off` (P4b S7),
   `receipt.attached`, `receipt.linked`, `receipt.unlinked`,
   `document.filed`, `attachment.withdrawn`, `attachment.text_extracted`,
-  `attachment.annotated`, `entry.settles` (P6) (plus the A/R, A/P, asset,
+  `attachment.annotated`, `entry.settles` (P6), `entry.draft_state_set`
+  (a draft building or awaiting its evidence: a note on the draft, no
+  figure) and `entry.draft_discarded` (a draft thrown away, with why; the
+  draft's earlier lines stay in the journal) (P4, feature `drafts_v2`)
+  (plus the A/R, A/P, asset,
   period, payroll, and class events listed on `JournalLine`).
 - `payload`: the full domain facts (account fields, entry with lines, blob
   sha, ...). Everything the applier needs; nothing it must look up elsewhere.