Add cancel reason when cancelling a job

Users want to capture a reason when cancelling a job so the team has a record of why the cancellation happened. Right now they can cancel but there is no place to record the reason, which makes it harder to track patterns and answer questions later.

New transcript context: The team specifically called out a gap between quote rejection and inspection cancellation. Quote rejection already supports a reason, but scheduled inspections can be cancelled without capturing why. They use recurring reporting for leadership and want to understand why inspections were lost after scheduling, so they are currently considering custom-field workarounds to preserve that data.

Why it matters: Improves visibility into cancellations for client care, managers, and reporting without relying on notes or memory.