Give local and Docker automation runs the same conversation execution contract

[neubig]

Desired Behavior

Automation bundles must use the same execution contract for local and Docker workspaces. The initial Docker dispatcher provisions a conversation and supplies AUTOMATION_CONVERSATION_ID, but the local backend only supplies a workspace and server credential. Move conversation provisioning and environment construction into a shared backend contract, leaving only runtime resource acquisition/release and credential selection specific to workspace kind. Preserve existing local deployments that do not request a conversation profile.

Acceptance Criteria

• A configured automation profile provisions the same run-scoped conversation and environment variables for local and Docker workspaces.
• The selected workspace kind only affects backend provisioning, credentials, and cleanup; bundle logic does not inspect it.
• Both modes expose the same run conversation ID and scoped execution endpoints, with runtime credentials selected safely for Docker.
• Local completion preserves its persistent server and conversation history; Docker completion releases only that run runtime.
• Contract tests exercise the same bundle-facing behavior for both workspace kinds and retain legacy local behavior when no profile is configured.

This issue is ready-for-dev. Follow-up to #449.

[github-actions]

✅ ready-for-dev label applied

This issue meets the readiness criteria and is ready for contribution.
A contributor can now open a PR that links this issue (Fixes #<number>).

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