docs(proposals): ProposalManager v1.5 design — session cache, finaliz… #1204

Job	Run time
Downstream import smoke (representative consumer symbols)	27s
AdCP storyboard runner — examples/seller_agent.py	31s
Postgres conformance tests (Postgres 16)	34s
Test Python 3.10	25s
Test Python 3.11	30s
Test Python 3.13	37s
AdCP storyboard runner — examples/multi_platform_seller (PlatformRouter)	31s
AdCP storyboard runner — v3 reference seller (translator)	15s
Validate schemas are up-to-date	25s
Test Python 3.12	37s
v3 reference seller — pytest (respx-mocked upstream)	26s
Validate conventional commit format	0s
	5m 18s

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