[Improve] Make original task prompts easy to copy

[roomote-roomote]

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

What changed

• Added an Original Prompt section at the top of Task Info on existing task pages.
• Used the durable task-level prompt so resumed runs still show the request that originally launched the task.
• Added the existing copy control with an explicit accessible label and bounded long-prompt display.
• Added focused coverage for rendering, copying, and tasks without an original prompt.

Why this change was made

The original request was only exposed as a conversation message with generic message actions, making it difficult to find and reuse. This task-page improvement complements #1605's Home-screen saved prompt library without duplicating that work.

Impact

Users can find and copy the original launch prompt from Task Info without searching the transcript, including after the task has resumed. Focused tests, web type-checking, linting, formatting, and repository pre-push checks pass. Browser screenshots could not be attached because the local proof session was redirected into account setup before any task page was reachable.

[roomote-community]

No code issues found. See task

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