chore(main): release 6.3.0-beta.6 #1867

Job	Run time
AdCP storyboard runner — v3 reference seller (translator)	2m 39s
v3 reference seller — pytest (respx-mocked upstream)	38s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.0)	2m 14s
Downstream import smoke (representative consumer symbols)	36s
Postgres conformance tests (Postgres 16)	1m 14s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 36s
Test Python 3.13	4m 58s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.1)	2m 20s
Validate schemas are up-to-date	1m 11s
Validate conventional commit format	11s
Test Python 3.11	5m 13s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 30s
Test Python 3.12	4m 59s
Test Python 3.10	4m 44s
AdCP storyboard runner — examples/seller_agent.py	3s
	34m 6s

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