Implements a sidebar hidden state and toggle functionality for fullscreen webview mode, including new CSS for sidebar transitions and a menu hint. Updates gamepad input handling to allow toggling the sidebar and scrolling in webview mode, and restricts focusable elements to the sidebar and header when browsing. Improves user experience when navigating and interacting with web content in fullscreen.
Introduces a new Big Picture Mode with a controller-friendly, console-style UI optimized for Steam Deck and handheld devices. Adds new renderer files (HTML, CSS, JS) for the mode, updates main and preload scripts to support window management and IPC for Big Picture Mode, and documents features and usage in BIG_PICTURE_MODE.md. Updates settings and navigation to allow launching and exiting Big Picture Mode.
andrew