The per-unit assessment (annual expenses / 12 / units) used the live association
unit count only. Add an override so the rate can use weighted/excluded units,
persisted on accounting.budget_workbooks.unit_override (null = live count). New
"# Units" control with a reset link; summary card and CSV use the effective count.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
