Refactor VPN configuration handling to remove device limit management

- Updated the VPN configuration commands and handlers to eliminate the device limit parameter, simplifying the configuration process.
- Adjusted related API documentation to reflect the removal of device limit management, clarifying that this setting is now handled directly in the 3x-ui by node administrators.
- Enhanced the overall codebase by removing unnecessary device limit references across various components, ensuring a cleaner and more maintainable code structure.

frontend/src/index.css

@@ -32,6 +32,14 @@
   --color-primary: var(--primary);
   --color-primary-foreground: var(--primary-foreground);
   --font-sans: system-ui, 'Segoe UI', Roboto, sans-serif;
+
+  /* +12.5% к дефолтной Tailwind-шкале (line-height — заданные Tailwind соотношения, масштабируются вместе с размером). */
+  --text-xs: 0.844rem;
+  --text-sm: 0.984rem;
+  --text-base: 1.125rem;
+  --text-lg: 1.266rem;
+  --text-xl: 1.406rem;
+  --text-2xl: 1.688rem;
 }
 
 @layer base {