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

crates/ledger-core/src/periods.rs

@@ -29,6 +29,35 @@ pub enum PeriodStatus {
     Closed,
 }
 
+/// Where a period close puts the period's net income.
+#[derive(Clone, Debug, PartialEq)]
+pub enum CloseTo {
+    /// One Retained Earnings account ([`RETAINED_EARNINGS_CODE`]): the
+    /// corporate convention.
+    RetainedEarnings,
+    /// Members' capital accounts, by share (shares sum to 1): the
+    /// partnership convention, where each member's capital account carries
+    /// their allocated earnings.
+    Members(Vec<(crate::AccountId, rust_decimal::Decimal)>),
+}
+
+/// Split `amount` by `shares` to the cent; the last share absorbs rounding,
+/// so the parts always sum to `amount` exactly.
+pub fn allocate(
+    amount: rust_decimal::Decimal,
+    shares: &[rust_decimal::Decimal],
+) -> Vec<rust_decimal::Decimal> {
+    use rust_decimal::RoundingStrategy::MidpointAwayFromZero;
+    let mut parts: Vec<_> = shares
+        .iter()
+        .map(|s| (amount * s).round_dp_with_strategy(2, MidpointAwayFromZero))
+        .collect();
+    if let Some((last, rest)) = parts.split_last_mut() {
+        *last = amount - rest.iter().copied().sum::<rust_decimal::Decimal>();
+    }
+    parts
+}
+
 /// Code of the Retained Earnings account that closing entries credit (or
 /// debit), created on the first close if the chart lacks it.
 pub const RETAINED_EARNINGS_CODE: &str = "3999";