TASK-018 TUI: Tabbed stack panel for News/Feeds/HN

Description

The News page currently shows 4 narrow columns: Headlines, Briefs, Feeds, HN. Collapse these into a single full-width tabbed panel where , / . (or number keys) cycle between tabs. This mirrors Glint's "stack" widget concept.

Tabs: Headlines | Briefs | Feeds | HN

Each tab renders the same content as the current panel, but with the full page width available. The active tab label is highlighted in the panel border title (e.g. News [ Headlines | Briefs | Feeds | HN ]).

The Personal page keeps its current layout; only page-news changes.

Implementation:

• Replace the 4-panel Horizontal in page-news with a single DashPanel wrapping a ContentSwitcher
• Border title shows tab strip
• , / . bindings cycle tabs (or 1-4 number keys scoped to the news page)
• Each tab's content uses the existing render functions with higher cap values

Acceptance Criteria

• #1 News page shows a single tabbed panel instead of 4 columns
• #2 Tab labels visible in panel border
• #3 Comma/period or number keys cycle tabs
• #4 Each tab shows correct content at full page width
• #5 Personal page layout unchanged