fix(pat): carry agentCode in batch auth args

[shangguanxuan633-lab]

Summary

• Carry agentCode and sessionId in pat.batch_plan / pat.batch_grant arguments.
• Add DWS_DINGTALK_AGENTCODE as a compatibility alias while keeping DINGTALK_DWS_AGENTCODE priority.
• Keep backward compatibility with older gateways that reject identity args by retrying without identity args while preserving env context.

Tests

• go test ./internal/pat ./internal/auth
• go test ./internal/app -run 'TestResolveIdentityHeadersForwards(Compat)?AgentCode|TestDefaultPATServerDescriptorUsesBehaviorAuthorizationName|TestDirectRuntimeEndpoint_DefaultPATFallback|TestDirectRuntimeEndpoint_PATDiscoveryOverride'\n- go test ./test/unit -run 'TestHostOwnsPATFlow_OnlySignal|TestPATStderrJSON|TestPATStderrJSON_CodeEnumFrozen'\n\n## Notes\nBranch is forked from DingTalk-Real-AI/dingtalk-workspace-cli:main; unrelated feat/dws-devapp PR was closed.