Simplify scheduling handlers by using bookings.total_duration_minutes and bookings.end_time computed columns instead of inline UNION sub-queries for duration calculations. Remove unnecessary ::text casts from end_time columns (using native timestamptz). Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>