Audit fixes: party money, reconciliations, require policy, K-1 property

An independent recompute of the real books found no numeric
disagreements; review found 15 defects, all fixed with spec-first
regression tests:

- k1: a prepaid credited straight to capital is property; a member
  paying a vendor through 2100 is cash. Docs and B-13 match.
- parties: a reversal of a reversal counts on its root's side;
  liability-to-liability payments (member pays the card) count as paid.
- viewer: party money uses the server's cash accounts and full calendar
  year; per-party "What for" scales multi-party entries.
- reconciliations: refuse a withdrawn statement before journaling; new
  books.void_statement; reconciled lines can't be un-cleared; one shared
  reconcilable-accounts rule for digest and viewer.
- CPA package includes receipts linked to entries; a file can't be both
  filed on and linked to one entry.
- parties = "require" covers payroll, tax remittance (agency) and
  disposal (buyer); no-party marks follow reversal chains and clear when
  a vendor is tagged.
- derived member shares are frozen to exact amounts when posted, so a
  settings change never re-splits history.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

docs/spec/rules.md

@@ -238,8 +238,12 @@ closed period).
   both in a statement's span are neither contributions nor
   distributions (`reports::cancelled_in_span`; the K-1 worksheet reads
   the same). The K-1 worksheet's contributed property (Item L) is what
-  the member owned and handed over, with its own basis (§723): never a
-  prepaid service they paid for the company (cash), and shared among
+  the member owned and handed over, with its own basis (§723): a prepaid
+  service contract credited straight to capital is property (a contract
+  handed over), while a prepaid service they paid a vendor for on the
+  company's behalf, booked through Due to Shareholders (Dr prepaid / Cr
+  2100, then Dr 2100 / Cr capital), is cash (DECISION, the owner,
+  2026-10-15); and it is shared among
   members credited in one entry in proportion to their credits
   (`k1` INVARIANTS 3, 4, 6).