feat: Implement responsive page layout components and CSS variables

- Added PageScaffold component for shared page layout with safe-area padding and scroll management.
- Introduced ResponsiveMobileShell for mobile canvas layout with customizable backgrounds.
- Created ScrollablePage component for scrollable content areas.
- Updated CSS styles for coins rules screen, sidebar components, and subscription sections to use responsive design tokens.
- Added viewport CSS variables provider to synchronize CSS variables with the visual viewport.
- Refactored breakpoints and dimensions for better responsiveness across devices.

src/app/_components/core/index.ts

@@ -5,6 +5,10 @@
 export * from "./bottom-sheet";
 export * from "./checkbox";
 export * from "./dialog";
+export * from "./fixed-bottom-area";
 export * from "./loading-indicator";
 export * from "./mobile-shell";
+export * from "./page-scaffold";
+export * from "./responsive-mobile-shell";
+export * from "./scrollable-page";
 export * from "./settings-section";