Feature request: add an fzf-like link picker for preview content

Is your feature request related to a problem? Please describe.

When reading an issue or pull request in the preview pane, links in the body and comments cannot be selected or opened from within gh-dash. I have to open the whole issue or PR in GitHub, find the same content, and locate the link again.

Describe the solution you'd like

Add a keyboard-driven link picker for the current preview with fzf-like filtering.

The picker could:

• collect links from the issue or PR body and comments;
• display each link's label and URL;
• filter links as the user types;
• open the selected link;
• provide a secondary action to copy its URL.

Describe alternatives you've considered

Terminal link handling only works when a URL is visible and recognized by the terminal. Markdown links may display only their label, while mouse-based handling does not provide the same keyboard-driven workflow.