Depreciation schedule with partial-month convention

Create a depreciation schedule and monthly depreciation JE.

Inputs:
- Asset register additions/disposals: {asset_register_changes}
- Depreciation method: {dep_method}  # SL/DB/units-of-production
- Convention: {partial_month_convention}
- Useful lives and salvage values: {lives_and_salvage}
- Periods needed: {periods}

Output:
1) Depreciation rollforward by asset class (Beg NBV, Adds, Disposals, Depreciation, End NBV).
2) Detailed schedule for new assets (in-service date, basis, rate, monthly dep).
3) Journal entry for the period with accounts and memo.
4) Tie-out checks and exceptions (negative NBV, missing dates, life anomalies).