chore(main): release 6.4.0 #2027

Job	Run time
Validate conventional commit format	14s
Postgres conformance tests (Postgres 16)	1m 14s
Downstream import smoke (representative consumer symbols)	37s
Validate schemas are up-to-date	20m 56s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 34s
v3 reference seller — pytest (respx-mocked upstream)	41s
Test Python 3.12	6m 37s
Test Python 3.10	6m 52s
Test Python 3.11	6m 35s
Test Python 3.13	6m 3s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.1)	2m 39s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 49s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.0)	2m 19s
AdCP storyboard runner — v3 reference seller (translator)	2m 43s
AdCP storyboard runner — examples/seller_agent.py	2s
	1h 0m 55s

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