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

crates/ledger-core/src/error.rs

@@ -35,6 +35,20 @@ pub enum LedgerError {
     #[error("journal line amount is out of range (at most 1000000000000000, ten decimal places)")]
     AmountOutOfRange,
 
+    /// An amount finer than its currency's smallest unit (ISO 4217 minor
+    /// units): no one can pay a fraction of a cent (rules.md B-3).
+    #[error(
+        "amount {amount} {currency} has more than {places} decimal places; round it to the {currency} minor unit first"
+    )]
+    FinerThanMinorUnit {
+        /// The amount as given.
+        amount: rust_decimal::Decimal,
+        /// Its currency code.
+        currency: String,
+        /// The decimal places the currency allows.
+        places: u32,
+    },
+
     /// The referenced account does not exist in the chart of accounts.
     #[error("unknown account id {0}")]
     UnknownAccount(u64),