Define the release process for the CLI and runtime tag lines

Part of #37. Came out of an ideation session, not a scoped request.

Splitting the runtime out means two independent version lines — the CLI at `vX.Y.Z` and the runtime at `/vX.Y.Z` — so the release flow and the compatibility policy between them need to be written down: what gets tagged when, whether a CLI version declares a runtime range it supports, and how a user upgrading one without the other is handled.

Start by reading the context in issue #37 and mapping the CLI and runtime tag lines described here. Define the release sequence, compatibility policy, supported runtime range, and upgrade behavior, then document the agreed process and verify that both independent version lines are covered.

Written by the indexing model from the issue text.