Background

Prototype confirmed: QRhiWidget (GPU-accelerated spectrum/waterfall) survives Qt widget reparenting into a floating top-level window. All rendering, signal connections, VFO overlays, and VITA-49 stream routing continue working after pop-out.

This builds on PR #916 (poppable applets by @chibondking) which established the FloatingAppletWindow pattern.

Feature

Right-click a panadapter title bar → "Pop out" detaches it into its own floating window. "Dock" returns it to the PanadapterStack splitter. Multi-monitor operators can put each pan on a different screen.

Implementation

Follow the FloatingAppletWindow pattern from #916:

1. Add popOutRequested(panId) and dockRequested(panId) signals to PanadapterApplet
2. Right-click context menu on pan title bar (Pop out / Dock)
3. On pop-out: reparent PanadapterApplet to a FloatingAppletWindow (or dedicated FloatingPanWindow)
4. On dock: reparent back into PanadapterStack's QSplitter
5. Persist float state + geometry per-pan via AppSettings
6. Auto-dock on pan removal (layout change, disconnect)

Proven by prototype

• QRhiWidget GPU rendering works in floating window ✓
• VFO overlays render correctly ✓
• FFT spectrum + waterfall both functional ✓
• Signal connections survive reparent ✓
• Overlay menu accessible ✓

Considerations

• Dock path needs to re-insert into the QSplitter at the correct position
• Layout changes (2v→2h, etc.) should auto-dock all floating pans first
• PanadapterStack::count() should still count floating pans
• Active pan tracking should work across floating/docked states