Add explicit deal type support for schedules

[anjor]

Summary

• add explicit dealType on schedule model (market or pdp)
• accept and validate dealType in schedule create/update handlers
• add CLI flags:
  • singularity deal schedule create --deal-type
  • singularity deal schedule update --deal-type
• make dealpusher honor schedule.dealType in default resolution (while keeping existing resolver override behavior)
• add tests for invalid deal type rejection and successful persistence

Validation

• go test ./handler/deal/schedule
• go test ./service/dealpusher
• go test ./cmd