feat(translation): list known keys in TranslationMap KeyError #1600

Job	Run time
Validate schemas are up-to-date	3m 51s
v3 reference seller — pytest (respx-mocked upstream)	43s
AdCP storyboard runner — examples/seller_agent.py	1m 22s
Test Python 3.11	3m 58s
Downstream import smoke (representative consumer symbols)	28s
AdCP storyboard runner — v3 reference seller (translator)	2m 5s
Test Python 3.13	4m 12s
Validate conventional commit format	42s
AdCP storyboard runner — sales-proposal-mode (proposal_finalize)	1m 10s
Postgres conformance tests (Postgres 16)	1m 8s
Test Python 3.12	4m 17s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 35s
Test Python 3.10	4m 23s
	29m 54s

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