test(signing): vendor the complete AdCP 3.1.8 request-signing vector set and pin it against drift #2112

Job	Run time
Validate conventional commit format	15s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.0)	1m 32s
Downstream import smoke (representative consumer symbols)	34s
Test Python 3.13	5m 38s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk latest)	1m 42s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 57s
v3 reference seller — pytest (respx-mocked upstream)	50s
Test Python 3.12	6m 5s
Test Python 3.11	5m 56s
Test Python 3.10	5m 51s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	2m 9s
Postgres conformance tests (Postgres 16)	1m 51s
Validate schemas are up-to-date	6m 36s
AdCP storyboard runner — v3 reference seller (translator)	2m 24s
AdCP storyboard runner — examples/seller_agent.py	2s
	43m 22s

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