test(CQ-ORCH-9): Add SpawnAgentDto validation tests
Adds 23 dedicated DTO-level validation tests for SpawnAgentDto and
AgentContextDto using plainToInstance + validate() from class-validator.
Covers: valid payloads, missing/empty taskId, invalid agentType, empty
repository/branch, empty workItems, shell injection in branch names,
SSRF in repository URLs, file:// protocol blocking, option injection,
and invalid gateProfile values.
Replaces the 5 controller-level validation tests removed in CQ-ORCH-9
with proper DTO-level equivalents.
Co-Authored-By: Claude Opus 4.6 <[email protected]>
