fix: preserve subscription enabled false

[ysyneu]

Summary

• make IncidentTriggerSubscriptionUpsertRequest hand-written so enabled=false survives JSON encoding
• skip the generated duplicate type and regenerate models
• add regression coverage for the explicit disabled subscription value

Verification

• make check
• go test ./... -run TestIncidentTriggerSubscriptionUpsertRequestPreservesDisabledValue -count=1
• go test ./... -count=1
• go generate ./...