fix: period close sweeps only through the period end; partnerships close into members' capital

The close zeroed every revenue and expense account's all-time movement,
so closing a period after later entries were posted swept those too:
close January in March and February's and March's income landed in
January's closing entry. The preview had the same bug and never showed
where the net went. Now:

- close_period_to(id, to) zeroes balances as of the period end; entries
  dated later stay open for their own period. Periods must close in
  order (LedgerError::CloseOutOfOrder): a later close has already swept
  the earlier period.
- CloseTo::Members: for a partnership (multi-member LLC) the net goes to
  each member's capital account by share, to the cent, the last member
  absorbing rounding, which is what K-1 capital accounts track.
  CloseTo::RetainedEarnings (3999) stays the default; close_period is
  shorthand for it. books.close_period picks Members when
  wanderbooks.toml lists members.
- The journal records the close target; replay re-derives the closing
  entry and now compares every line with the journal, not just the id,
  so a change to closing math can never silently rewrite history.
- The tool's preview is the real close run on a clone of the ledger
  (Ledger now derives Clone), so preview and post can't disagree.
- Members' equity: closing entries into a capital account are income,
  not contributions. Balance sheet for a partnership: capital accounts
  (with allocated earnings), then only unallocated earnings —
  "Undistributed earnings, prior years" if any, and this year's unclosed
  net income (loss). periods::allocate is shared by the close and the
  statement.

Tests: January closed after February is posted sweeps exactly Dr 4000
2,500 / Cr 6100 800 / Cr 3999 1,700 (mutation-checked: the old code gives
3,500/120/800/2,580); out-of-order close refused; a partnership close
splits 666.67 into 333.34/333.33 with no 3999, and the members' equity
statement reads correctly before and after; store replay of a members
close (reopen, rebuild, verify); partnership and corporate balance sheet
layouts; stdio close preview equals the posted lines.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

docs/mcp-interface.md

@@ -279,10 +279,13 @@ R-FUTURE-3 and rides the engine roadmap, not the MCP layer.
 - `books.create_period { name, start, end }` → `{ period_id }`.
   Dates are YYYY-MM-DD, inclusive.
 - `books.close_period { period_id, confirmed? }` → without confirmation:
-  `{ status: "preview", lines: [...] }` showing the closing lines and posts
-  nothing; with `confirmed: true`: posts the closing entry (revenue debited
-  to zero, expenses credited to zero, net to `3999` Retained Earnings) and
-  marks the period closed. Closed periods reject new entries.
+  `{ status: "preview", lines: [...] }`: the exact closing entry (the close
+  run on a copy of the ledger), posting nothing; with `confirmed: true`:
+  posts it and marks the period closed. The entry zeroes revenue and
+  expense balances as of the period end; the net goes to `3999` Retained
+  Earnings, or, with `[[company.members]]` in `wanderbooks.toml`, to each
+  member's capital account by share. Periods close in order. Closed periods
+  reject new entries.
 - `books.list_periods {}` → `{ periods: [{ id, name, start, end, status,
   closing_entry }] }`.