core: no entry posts a fraction of a cent; verify compares whole ledgers

CI's run of the store refusal property found a payroll run that posted
$65.27794: the employer tax was passed in unrounded and nothing refused
it, though rules.md B-3 already says a ledger in one money holds no
fractions of its smallest unit. Sums of it then differed in scale
between journal replay and the SQLite read-back.

- Ledger::post_entry refuses any line finer than its currency's ISO 4217
  minor unit (FinerThanMinorUnit), whatever made the line: payroll,
  closes, disposals. add_line refuses it up front. Older journals replay
  as booked through replay_post_entry. Spec tests for the kernel's
  ten-place limit now run on the replay path.
- The property's body is now run_ops, so failing sequences become named
  regression tests (regression_payroll_with_a_fraction_of_a_cent). The
  generator rounds payroll tax to the cent, as callers must.
- Ledger derives PartialEq and gains differs_from; Store::verify compares
  the live ledger with the journal replay in full (drafts, documents,
  schedules, periods, settings), not just balances, and names the parts
  that differ. The property checks the ledger its commands built against
  that replay and against the reopened books.

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

docs/spec/rules.md

@@ -66,10 +66,14 @@ match a bank statement: DECISION (Stephen, 2026-10-13), after the GnuCash
 cross-check found wanderbooks kept $108.34567 where GnuCash booked
 $108.35. Lines booked before then replay as booked.
 
-**Enforced:** `Ledger::add_line` (base currency only),
-`Ledger::add_line_fx` (base amount = foreign amount × rate, rounded to
-the minor unit; original kept). **Checked:**
-`a_foreign_line_is_booked_in_whole_base_units`; the GnuCash oracle.
+**Enforced:** `Ledger::add_line` (base currency only, no fraction of the
+minor unit), `Ledger::add_line_fx` (base amount = foreign amount × rate,
+rounded to the minor unit; original kept), `Ledger::post_entry` (every
+line, whatever made it: payroll, closes, disposals; `FinerThanMinorUnit`,
+since 2026-10-13 after a payroll run posted $65.27794). Journals from
+before replay as booked (`replay_post_entry`). **Checked:**
+`a_foreign_line_is_booked_in_whole_base_units`,
+`no_entry_posts_a_fraction_of_the_minor_unit`; the GnuCash oracle.
 **Checked:** `foreign_currency_line_is_rejected`, `fx_overflow_is_an_error`.
 
 ## B-4 Five elements, closed list