Support opening reports and plans when there are multiple in a session #5349

Describe the feature or problem you'd like to solve

The ctrl+y key binding opens the plan, or the most recent report only if there is no plan. There is no way to reference or open other reports that have been generated previously, or any reports after a plan has been generated.

Proposed solution

An /open command to provide a pick-list of the reports and plans that have been generated during the conversation, shown in chronological order. Picking one of them opens that markdown file using the normal viewer.

Example prompts or workflows

1. Run a /research command on a topic, and see that it generates a markdown report
2. Run another /research command on a different topic, and see that it genrates a markdown report.The Ctrl+y opens only the most recent report markdown.
3. Use the (proposed) /open slash-command, and pick the older research report to view. Exit viewing when done.
4. Run a /plan command, and see it generates a markdown plan and that Ctrl+y can only open it.
5. Run a /research command to ask probing questions about something in the plan. See that it creates a research markdown report, but ctrl+y is can still only open the plan.
6. Use the (proposed) /open slash-command, and pick the first, second, or most recent research report to view.

Additional context

There's currently only a ctrl+y key binding to show a markdown file that generated by the session. If a plan has been generated, that markdown file is always used instead of any research reports. There is no way to select which markdown file when there are multiple present.

The current solution is to locate the full report file name listed in the history, and copy the path from the history output. Then open that file manually using some other tool.

This is particularly annoying if you ran any /research commands after having generated a plan, because all new research reports are effectively inaccessible.