P3: depreciation straight-line by days through the final month, schedules by day (defects 22, 9, D-37)

The final month takes what the months before leave, spread over its days;
a disposed asset stops on its disposal day. A skipped month is caught up
in the month the run is made; a reversed run un-posts its month. New
schedules spread by day; equal-months schedules must start on the 1st.
Amounts round to the currency's own minor unit. Kani and Lean proofs; an
exhaustive search over runs, reversals and disposals.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-store/tests/attachments.rs

@@ -366,6 +366,7 @@ fn every_subject(s: &mut Store, fx: &Fx) -> Vec<Subject> {
             months: 12,
             balance_account: prepaid,
             pl_account: fx.expense,
+            convention: ledger_core::ScheduleConvention::MonthlyEven,
         })
         .unwrap();
     clear_jan(s, fx);