chore(main): release 6.3.0 #2019

Job	Run time
Postgres conformance tests (Postgres 16)	1m 19s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.0)	2m 33s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.1)	2m 42s
Validate schemas are up-to-date	21m 0s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 44s
Test Python 3.10	6m 55s
Downstream import smoke (representative consumer symbols)	1m 7s
Test Python 3.13	6m 20s
v3 reference seller — pytest (respx-mocked upstream)	40s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 51s
Test Python 3.11	6m 46s
Test Python 3.12	6m 41s
AdCP storyboard runner — v3 reference seller (translator)	2m 57s
Validate conventional commit format	-1s
AdCP storyboard runner — examples/seller_agent.py	3s
	1h 2m 37s

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