Fill automation gaps in existing conversation and workspace APIs

[neubig]

Desired Behavior

Automation dispatch and workflow bundles should use the existing SDK conversation/workspace interfaces. Fill the missing Python entry points without introducing a parallel AgentServerClient/RuntimeClient hierarchy or a second HTTP request layer.

Acceptance Criteria

• RemoteConversation has explicit create(workspace, StartConversationRequest) and attach(workspace, id) methods. Neither falls back to the other; the constructor keeps requiring an agent. Creation reuses canonical request/profile resolution and all paths share connection, messaging, run, event, and interruption machinery.
• Existing remote workspaces expose conversation-scoped file/command operations and separate command start/output retrieval, sharing the request generators already used by execute_command.
• Conversation-scoped runtime credentials and resource release use SDK workspace methods; unrelated or missing scope cannot become a host-runtime fallback.
• Automation consumers stop importing the parallel SDK clients; extensions use explicit RemoteConversation.attach and the existing lifecycle.
• Existing SDK APIs remain compatible. Sync/async scope and lifecycle tests pass; isolated local/Docker demonstration exercises the explicit methods.

This issue is ready-for-dev. Server/runtime prerequisites: #4966 and #3403. Consumers: OpenHands/automation#449/#453 and OpenHands/extensions#570–#573. Documentation: OpenHands/docs#793.

Implemented in #5010 (4bbab2dd0) with migrated consumers. Fresh isolated Canvas before/after + local/Docker evidence passed with the same bundle, real model turns, exact docs examples, and missing-attach no-creation verification. 288 SDK regressions pass. Merge/release dependencies and current CI/review status remain recorded in the PR.

[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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