[Improve] Show task summaries in Session execution details

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Added task summaries to the Fast Session execution details sidebar using the existing summary query and markdown rendering path.
• Made legacy Fast-only task cards resolve their full task details on selection and open the same execution details panel.
• Added loading skeletons, stale-summary refresh, retryable errors, latest-output fallback, in-progress and terminal empty states, and access-aware behavior.
• Expanded Session workspace client coverage for each summary state, action, and the Fast-only selection path.

Why this change was made

Execution details previously stopped after basic metadata and the workspace link, forcing users to open the full task workspace to understand what happened. Legacy Fast-only Sessions also exposed lightweight task cards that could not reach the execution-details route. The sidebar now provides a concise result in context without introducing a separate summary implementation.

Impact

Users can review the goal, decisions, and outcome of an execution directly from unified and legacy Fast-only Sessions. Existing task access restrictions remain intact, and sparse or unavailable summaries degrade to useful status copy or the latest execution output.

Browser screenshots are not included because the local authenticated product surface was blocked by the inference-provider setup gate; automated client coverage verifies the rendered states and interactions.

[roomote-community]

No code issues found. See task

• Fast-only sessions cannot show a summary (apps/web/src/app/(sandbox)/sessions/[sessionId]/SessionWorkspace.tsx:211).

_{Reviewed 0750fe3}

[roomote-roomote]

Fixed the Fast-only Session path so selected task cards load full execution details and render the existing summary panel. The regression test, full web client suite, lint, typechecking, and pre-push gates pass in commit 0750fe3. Browser proof remains blocked by the local onboarding provider setup gate. See review task.