feat(server): CallableSubdomainTenantRouter for DB-backed tenant lookups #1195

Job	Run time
Downstream import smoke (representative consumer symbols)	25s
v3 reference seller — pytest (respx-mocked upstream)	42s
AdCP storyboard runner — v3 reference seller (translator)	1m 29s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	1m 26s
Test Python 3.10	3m 40s
Test Python 3.13	3m 23s
Test Python 3.12	3m 33s
AdCP storyboard runner — examples/seller_agent.py	1m 21s
Validate conventional commit format	6s
Postgres conformance tests (Postgres 16)	1m 5s
Test Python 3.11	3m 29s
Validate schemas are up-to-date	3m 33s
	24m 12s

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