chore(main): release 6.3.0 #2018

Job	Run time
AdCP storyboard runner — v3 reference seller (translator)	2m 41s
Validate conventional commit format	16s
Downstream import smoke (representative consumer symbols)	59s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 37s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	2m 3s
Postgres conformance tests (Postgres 16)	1m 25s
v3 reference seller — pytest (respx-mocked upstream)	44s
Test Python 3.11	6m 0s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.0)	2m 19s
Test Python 3.10	6m 48s
AdCP storyboard runner — examples/seller_agent.py (@adcp/sdk adcp-3.1)	2m 38s
Test Python 3.12	7m 36s
Test Python 3.13	6m 18s
Validate schemas are up-to-date	20m 57s
AdCP storyboard runner — examples/seller_agent.py	2s
	1h 2m 23s

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