feat: mobile-first responsive overhaul — safe areas, touch targets, bottom sheet, bottom nav

Viewport:
- Add `viewport` export with `viewport-fit=cover` (enables CSS safe-area-inset-*
  on bezel-less iOS/Android) and `interactive-widget=resizes-content` (prevents
  layout jumps from virtual keyboard open/close)

iOS zoom prevention:
- input.tsx, textarea.tsx: change text-sm (14px) → text-base sm:text-sm (16px)
  on mobile; iOS Safari auto-zooms any input with font-size < 16px

Touch targets:
- button.tsx: default h-10 → h-11 (44px), sm h-8 → h-9 (36px), icon h-10→h-11
  matching the 44×44px iOS HIG and WCAG 2.5.5 minimum
- Add touch-manipulation to buttons, inputs, textarea to eliminate 300ms tap delay

Dialog → mobile bottom sheet:
- On mobile (< 640px): anchored to bottom with full width, rounded top corners,
  slide-in-from-bottom / slide-out-to-bottom animation, drag handle affordance,
  max-h-[90svh] + overflow-y-auto to prevent viewport overflow
- Safe area padding: pb-[max(1.25rem,env(safe-area-inset-bottom))]
- On desktop (sm+): unchanged centered modal with zoom animation
- Close button gets a 32×32 tap area on mobile

Mobile navigation:
- New bottom-nav.tsx: persistent 3-tab bottom bar (مسیر/مرکز/لیگ) shown below
  md: breakpoint, hidden on desktop; 56px height + safe-area-inset-bottom;
  active tab gets heavier stroke and scale
- Only shown for authenticated non-admin users
- app-shell.tsx: injects BottomNav; main content gets dynamic padding-bottom to
  clear the bar (56px + safe area) on mobile, reverts to py-10 on md:
- Footer: safe-area-inset-bottom padding so content clears iPhone home indicator

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/ui/button.tsx

@@ -4,7 +4,7 @@ import { cva, type VariantProps } from "class-variance-authority";
 import { cn } from "@/lib/utils";
 
 const buttonVariants = cva(
-  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-lg border font-sans text-sm font-bold transition-all duration-300 ease-[var(--ease-soft)] focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0 cursor-pointer select-none active:translate-y-px active:shadow-none",
+  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-lg border font-sans text-sm font-bold transition-all duration-300 ease-[var(--ease-soft)] focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0 cursor-pointer select-none active:translate-y-px active:shadow-none touch-manipulation",
   {
     variants: {
       variant: {
@@ -18,10 +18,10 @@ const buttonVariants = cva(
         link: "border-transparent text-primary underline-offset-4 hover:underline",
       },
       size: {
-        default: "h-10 rounded-lg px-4 py-2",
-        sm: "h-8 rounded-lg px-3 text-xs",
+        default: "h-11 rounded-lg px-4 py-2",
+        sm: "h-9 rounded-lg px-3 text-xs",
         lg: "h-[3.25rem] rounded-2xl px-7 text-base",
-        icon: "h-10 w-10 rounded-xl",
+        icon: "h-11 w-11 rounded-xl",
       },
     },
     defaultVariants: { variant: "default", size: "default" },