Description

News, Feeds, and HN items already carry URLs that are clickable via app.open_link. Add a keyboard path: when an item is selected (via arrow keys), pressing o or Enter opens its URL in the default browser.

Implementation:

• In the item-navigation layer (from TASK-007), store the URL alongside each selectable item
• Bind o (and Enter where it won't conflict) to app.open_url(selected_item.url)
• Show a brief toast notification: "Opening: {title[:50]}"
• Items without URLs (e.g. calendar events, todos) do nothing on o / show a "no link" toast

Depends on: TASK-007 (keyboard-navigable items)

Acceptance Criteria

• #1 o or Enter on a selected news/feed/HN item opens its URL in the browser
• #2 Toast confirms the open action
• #3 Items without URLs show a graceful no-op or message
• #4 Existing mouse-click link behavior unchanged