feat(frontend): Responsive Smartphone-Oberfläche (Modul 15)

Mobile Bottom-Navigation und permanent erreichbare "+ Neu"-
Schnellaktion (Durchsicht/Varroa/Behandlung/Fütterung/Aufgabe/Ernte).
Header-Navigation überarbeitet, damit sie bei schmaler Breite intern
scrollt statt die Seite horizontal zu sprengen. Verifiziert bei
Smartphone- (390px) und Tablet-Breite (820px).

ApiCore-Frontend/src/app/(app)/bottom-nav.tsx

@@ -0,0 +1,39 @@
+"use client";
+
+import Link from "next/link";
+import { usePathname } from "next/navigation";
+import { LayoutDashboard, Layers, ListTodo, Search } from "lucide-react";
+import { cn } from "@/lib/utils";
+
+const ITEMS = [
+  { label: "Start", href: "/dashboard", icon: LayoutDashboard },
+  { label: "Völker", href: "/colonies", icon: Layers },
+  { label: "Aufgaben", href: "/tasks", icon: ListTodo },
+  { label: "Suche", href: "/search", icon: Search },
+];
+
+export function BottomNav() {
+  const pathname = usePathname();
+
+  return (
+    <nav className="fixed inset-x-0 bottom-0 z-30 flex border-t bg-background sm:hidden">
+      {ITEMS.map((item) => {
+        const Icon = item.icon;
+        const isActive = pathname.startsWith(item.href);
+        return (
+          <Link
+            key={item.href}
+            href={item.href}
+            className={cn(
+              "flex flex-1 flex-col items-center gap-1 py-2 text-xs",
+              isActive ? "text-primary" : "text-muted-foreground",
+            )}
+          >
+            <Icon className="size-5" />
+            {item.label}
+          </Link>
+        );
+      })}
+    </nav>
+  );
+}

ApiCore-Frontend/src/app/(app)/layout.tsx

@@ -5,6 +5,8 @@ import Link from "next/link";
 import { useRouter } from "next/navigation";
 import { useAuth } from "@/lib/auth/auth-context";
 import { Button } from "@/components/ui/button";
+import { BottomNav } from "./bottom-nav";
+import { QuickAddMenu } from "./quick-add-menu";
 
 export default function AppLayout({ children }: { children: ReactNode }) {
   const router = useRouter();
@@ -22,9 +24,10 @@ export default function AppLayout({ children }: { children: ReactNode }) {
 
   return (
     <div className="flex min-h-screen flex-col">
-      <header className="flex items-center justify-between border-b px-4 py-3">
-        <nav className="flex items-center gap-4">
-          <span className="font-semibold">ApiCore</span>
+      <header className="flex items-center justify-between gap-3 border-b px-4 py-3">
+        <nav className="flex min-w-0 items-center gap-4 max-sm:gap-2">
+          <span className="shrink-0 font-semibold">ApiCore</span>
+          <div className="hidden min-w-0 items-center gap-4 overflow-x-auto whitespace-nowrap sm:flex">
           <Link className="text-sm text-muted-foreground hover:text-foreground" href="/dashboard">
             Dashboard
           </Link>
@@ -60,9 +63,12 @@ export default function AppLayout({ children }: { children: ReactNode }) {
               Benutzer
             </Link>
           ) : null}
+          </div>
         </nav>
-        <div className="flex items-center gap-3 text-sm">
-          <span className="text-muted-foreground">{user.email}</span>
+        <div className="flex shrink-0 items-center gap-3 text-sm">
+          <span className="hidden max-w-40 truncate text-muted-foreground md:inline">
+            {user.email}
+          </span>
           <Button
             variant="outline"
             size="sm"
@@ -74,7 +80,9 @@ export default function AppLayout({ children }: { children: ReactNode }) {
           </Button>
         </div>
       </header>
-      <div className="flex-1">{children}</div>
+      <div className="flex-1 pb-16 sm:pb-0">{children}</div>
+      <BottomNav />
+      <QuickAddMenu />
     </div>
   );
 }

ApiCore-Frontend/src/app/(app)/quick-add-menu.tsx

@@ -0,0 +1,45 @@
+"use client";
+
+import Link from "next/link";
+import { Plus } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import {
+  DropdownMenu,
+  DropdownMenuContent,
+  DropdownMenuItem,
+  DropdownMenuTrigger,
+} from "@/components/ui/dropdown-menu";
+
+const QUICK_ACTIONS = [
+  { label: "Durchsicht", href: "/inspections/new" },
+  { label: "Varroa-Messung", href: "/varroa/new" },
+  { label: "Behandlung", href: "/treatments/new" },
+  { label: "Fütterung", href: "/feedings/new" },
+  { label: "Aufgabe", href: "/tasks/new" },
+  { label: "Ernte", href: "/harvests/new" },
+];
+
+export function QuickAddMenu() {
+  return (
+    <DropdownMenu>
+      <DropdownMenuTrigger
+        render={
+          <Button
+            size="icon-lg"
+            className="fixed right-4 bottom-20 z-40 rounded-full shadow-lg sm:hidden"
+            aria-label="Neu"
+          />
+        }
+      >
+        <Plus className="size-6" />
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="end" side="top">
+        {QUICK_ACTIONS.map((action) => (
+          <DropdownMenuItem key={action.href} render={<Link href={action.href} />}>
+            {action.label}
+          </DropdownMenuItem>
+        ))}
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+}