feat(adagents): add validate_adagents_structure helper #1498

Job	Run time
Validate conventional commit format	11s
AdCP storyboard runner — examples/seller_agent.py	1m 19s
Postgres conformance tests (Postgres 16)	1m 0s
Downstream import smoke (representative consumer symbols)	30s
Validate schemas are up-to-date	2m 56s
v3 reference seller — pytest (respx-mocked upstream)	41s
AdCP storyboard runner — v3 reference seller (translator)	1m 52s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 6s
Test Python 3.13	3m 39s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 43s
Test Python 3.11	3m 31s
Test Python 3.10	3m 30s
Test Python 3.12	3m 47s
	25m 45s

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