feat(default-skin): Global controller overlay scale & opacity settings #2890

Overview

Add a global scale slider for the on-screen controller overlay, allowing users to make the entire controller HUD larger or smaller. This directly addresses the original request in #1602 where controls are reported as too small on some iPads.

User Story

As an iPad user, I want to scale the on-screen controller overlay so that buttons are comfortably sized for my hands and device.

Implementation Notes

• Add a controllerScale preference (Float, range 0.5–2.0, default 1.0) to PVSettings
• Apply the scale factor to the default programmatic skin and the legacy UIKit overlay (PVControllerViewController / PVGameControllerContainerView)
• Expose via:
  • Settings → Controller → "Overlay Scale" slider
  • Optional: in-game pinch-to-scale gesture on the overlay
• Persist per-system or globally (start with global, per-system is a stretch goal)
• Also add a global opacity setting (0–100%) while touching this area

Acceptance Criteria

• Scale slider available in Settings
• Controller overlay respects scale at launch and after live changes
• Scale persists across app restarts
• No visual clipping or layout breakage at min/max scale values

Part Of

Part of #2889 ([Epic] On-Screen Controller Customization)

Closes #1602