feat(arayüz): logo ve uygulama ikonları

- Logo: indigo zemin, spiral defter ve ¥ (frontend/brand/*.svg)
- scripts/icons.sh (npm run icons): favicon (svg/ico), PWA 192/512, maskable, Apple touch icon, Tauri 1024
- Logo bileşeni (components/logo.tsx)
- index.html: ikon bağlantıları, theme-color, açıklama

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -1,5 +1,6 @@
 import { useEffect, useState } from 'react'
 import { Plus } from 'lucide-react'
+import { Logo } from '@/components/logo'
 import { ThemeToggle } from '@/components/theme-toggle'
 import { Button } from '@/components/ui/button'
 import { formatDate, formatMoney, formatQuantity, toIsoDate } from '@/lib/format'
@@ -25,7 +26,9 @@ export default function App() {
     <main className="mx-auto flex max-w-3xl flex-col gap-8 px-4 py-8">
       <header className="flex flex-wrap items-center justify-between gap-4">
         <div>
-          <h1 className="text-3xl font-bold tracking-tight">📒 Kakeibo</h1>
+          <h1>
+            <Logo size={44} withText />
+          </h1>
           <p className="text-muted-foreground">Tasarım sistemi önizlemesi</p>
         </div>
         <ThemeToggle />

frontend/src/components/logo.tsx

@@ -0,0 +1,67 @@
+import { useId } from 'react'
+import { cn } from '@/lib/utils'
+
+/**
+ * Kakeibo logosu (kaynak: `frontend/brand/logo.svg` — ikisi aynı tutulmalı).
+ * `withText` ile yanında "Kakeibo" yazısı gösterilir.
+ */
+export function Logo({
+  size = 32,
+  withText = false,
+  className,
+}: {
+  size?: number
+  withText?: boolean
+  className?: string
+}) {
+  // Sayfada birden fazla logo olursa gradient kimlikleri çakışmasın
+  const gradientId = useId()
+
+  return (
+    <span className={cn('inline-flex items-center gap-2.5', className)}>
+      <svg
+        viewBox="0 0 512 512"
+        width={size}
+        height={size}
+        role="img"
+        aria-label={withText ? undefined : 'Kakeibo'}
+        aria-hidden={withText || undefined}
+        className="shrink-0"
+      >
+        <defs>
+          <linearGradient id={gradientId} x1="0" y1="0" x2="0" y2="1">
+            <stop offset="0" stopColor="#3b4aa8" />
+            <stop offset="1" stopColor="#26307a" />
+          </linearGradient>
+        </defs>
+        <rect width="512" height="512" rx="112" fill={`url(#${gradientId})`} />
+        <rect x="140" y="92" width="252" height="328" rx="28" fill="#f7f3ea" />
+        <rect x="140" y="92" width="52" height="328" rx="28" fill="#e6dfcf" />
+        <rect x="166" y="92" width="26" height="328" fill="#e6dfcf" />
+        <g fill="#26307a">
+          <circle cx="140" cy="150" r="13" />
+          <circle cx="140" cy="220" r="13" />
+          <circle cx="140" cy="290" r="13" />
+          <circle cx="140" cy="360" r="13" />
+        </g>
+        <g
+          fill="none"
+          stroke="#26307a"
+          strokeWidth="22"
+          strokeLinecap="round"
+          strokeLinejoin="round"
+        >
+          <path d="M238 178 L292 254 L346 178" />
+          <path d="M292 254 V342" />
+          <path d="M250 266 H334" />
+          <path d="M250 304 H334" />
+        </g>
+      </svg>
+      {withText && (
+        <span className="font-bold tracking-tight" style={{ fontSize: size * 0.6 }}>
+          Kakeibo
+        </span>
+      )}
+    </span>
+  )
+}