feat: Linear-style UI redesign with improved mobile experience

Major changes:
- Redesign cabinet with Linear-style components and top navigation
- Replace detail modals with dedicated pages (users, broadcasts, email templates)
- Add email channel support for broadcasts
- Remove pull-to-refresh, improve drag-and-drop on touch devices
- Fix Telegram Mini App: fullscreen, back button, scroll restoration
- Unify admin pages color scheme to design system
- Mobile-first improvements: horizontal tabs for settings, better touch targets

src/components/primitives/Popover/Popover.tsx

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+import * as PopoverPrimitive from '@radix-ui/react-popover';
+import { motion } from 'framer-motion';
+import { forwardRef, type ComponentPropsWithoutRef } from 'react';
+import { cn } from '@/lib/utils';
+import { dropdown, dropdownTransition } from '../../motion/transitions';
+
+// Close icon
+const CloseIcon = () => (
+  <svg width="16" height="16" viewBox="0 0 16 16" fill="none">
+    <path
+      d="M12 4L4 12M4 4l8 8"
+      stroke="currentColor"
+      strokeWidth="1.5"
+      strokeLinecap="round"
+      strokeLinejoin="round"
+    />
+  </svg>
+);
+
+// Root
+export const Popover = PopoverPrimitive.Root;
+
+// Trigger
+export const PopoverTrigger = PopoverPrimitive.Trigger;
+
+// Anchor
+export const PopoverAnchor = PopoverPrimitive.Anchor;
+
+// Close
+export const PopoverClose = PopoverPrimitive.Close;
+
+// Content
+export interface PopoverContentProps extends ComponentPropsWithoutRef<
+  typeof PopoverPrimitive.Content
+> {
+  showCloseButton?: boolean;
+}
+
+export const PopoverContent = forwardRef<HTMLDivElement, PopoverContentProps>(
+  (
+    { className, children, align = 'center', sideOffset = 4, showCloseButton = false, ...props },
+    ref,
+  ) => (
+    <PopoverPrimitive.Portal>
+      <PopoverPrimitive.Content
+        ref={ref}
+        align={align}
+        sideOffset={sideOffset}
+        className={cn(
+          'z-50 w-72 overflow-hidden',
+          'rounded-linear-lg border border-dark-700/50 bg-dark-900/95 backdrop-blur-linear',
+          'p-4 text-dark-100 shadow-linear-lg outline-none',
+          className,
+        )}
+        asChild
+        {...props}
+      >
+        <motion.div
+          variants={dropdown}
+          initial="initial"
+          animate="animate"
+          exit="exit"
+          transition={dropdownTransition}
+        >
+          {children}
+          {showCloseButton && (
+            <PopoverPrimitive.Close
+              className={cn(
+                'absolute right-2 top-2 rounded-linear p-1.5',
+                'text-dark-400 opacity-70 transition-all',
+                'hover:bg-dark-800/80 hover:opacity-100',
+                'focus:outline-none focus:ring-2 focus:ring-accent-500/50',
+              )}
+            >
+              <CloseIcon />
+              <span className="sr-only">Close</span>
+            </PopoverPrimitive.Close>
+          )}
+        </motion.div>
+      </PopoverPrimitive.Content>
+    </PopoverPrimitive.Portal>
+  ),
+);
+
+PopoverContent.displayName = 'PopoverContent';
+
+// Arrow
+export type PopoverArrowProps = ComponentPropsWithoutRef<typeof PopoverPrimitive.Arrow>;
+
+export const PopoverArrow = forwardRef<SVGSVGElement, PopoverArrowProps>(
+  ({ className, ...props }, ref) => (
+    <PopoverPrimitive.Arrow ref={ref} className={cn('fill-dark-800', className)} {...props} />
+  ),
+);
+
+PopoverArrow.displayName = 'PopoverArrow';

src/components/primitives/Popover/index.ts

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+export {
+  Popover,
+  PopoverTrigger,
+  PopoverAnchor,
+  PopoverClose,
+  PopoverContent,
+  PopoverArrow,
+  type PopoverContentProps,
+  type PopoverArrowProps,
+} from './Popover';