feat(mobile): mobile-responsive UI — bottom tab bar, bottom-sheet dialogs, PWA

All changes are gated behind max-md:/md:hidden so the >=768px desktop layout is untouched (verified with lint + build + live checks at 375px).

- globals.css: one mobile block — 16px inputs (no iOS auto-zoom), units sidebar stacks above content, wizard item rows become 2-col (text fields full-width, delete button full-width), dd-panels / flow diagram / conv-form stack, larger touch targets
- ui/dialog.tsx: dialogs become full-width bottom sheets on mobile (all modals inherit it); desktop keeps the centered dialog
- Header: sticky on mobile only + PageLayout bottom clearance
- New MobileTabBar: role-aware bottom tabs (office admin/manager, inventory PM, inventory admin); hidden on /wizard
- Wizard step 4: TouchSensor (150ms delay) so touch drag works without stealing scroll
- JalaliDatePicker: dropdown capped to viewport; bigger day cells and time inputs on mobile
- PWA: manifest.webmanifest + 192/512 icons (scripts/gen-pwa-icons.ps1) + theme-color/manifest links in index.html
- New docs/mobile-responsive.md documenting the full change set

frontend/src/components/layout/Header.tsx

@@ -27,7 +27,7 @@ export function Header({ title, sub, backTo, backLabel = "بازگشت", actions
   };
 
   return (
-    <header className="flex flex-wrap items-center gap-3 border-b border-line bg-panel px-5 py-2.5">
+    <header className="flex flex-wrap items-center gap-3 border-b border-line bg-panel px-5 py-2.5 max-md:sticky max-md:top-0 max-md:z-40">
       {menu && <div className="flex shrink-0 items-center">{menu}</div>}
       {(icon || brand) && (
         <span className="flex h-8 w-8 shrink-0 items-center justify-center rounded-lg bg-accent-bg text-accent">
@@ -38,7 +38,7 @@ export function Header({ title, sub, backTo, backLabel = "بازگشت", actions
         <button
           type="button"
           onClick={goBack}
-          className="inline-flex cursor-pointer items-center gap-0.5 rounded-md px-2 py-1 text-[13px] text-muted transition-colors hover:bg-slate-bg hover:text-ink"
+          className="inline-flex cursor-pointer items-center gap-0.5 rounded-md px-2 py-1 text-[13px] text-muted transition-colors hover:bg-slate-bg hover:text-ink max-md:px-2.5 max-md:py-2"
         >
           <ChevronRight className="h-4 w-4" />
           {backLabel}
@@ -64,6 +64,6 @@ export function PageLayout({
   className?: string;
 }) {
   return (
-    <div className={cn("mx-auto w-full max-w-[1200px] px-4 py-4", className)}>{children}</div>
+    <div className={cn("mx-auto w-full max-w-[1200px] px-4 py-4 max-md:pb-24", className)}>{children}</div>
   );
 }