패키지 버전 업데이트 및 SvelteKit 3, Tailwind CSS 4로 마이그레이션

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

src/app.css

@@ -1,3 +1,48 @@
-@import "tailwindcss/base";
-@import "tailwindcss/components";
-@import "tailwindcss/utilities";
+@import "tailwindcss";
+
+@theme {
+  --color-primary-100: #ffe3e3;
+  --color-primary-200: #ffc9c9;
+  --color-primary-300: #ffa8a8;
+  --color-primary-400: #ff8787;
+  --color-primary-500: #ff6b6b;
+  --color-primary-600: #fa5252;
+  --color-primary-700: #f03e3e;
+  --color-primary-800: #e03131;
+  --color-primary-900: #c92a2a;
+  --color-primary-000: #fff5f5;
+
+  --color-gray-100: #f1f3f5;
+  --color-gray-200: #e9ecef;
+  --color-gray-300: #dee2e6;
+  --color-gray-400: #ced4da;
+  --color-gray-500: #adb5bd;
+  --color-gray-600: #868e96;
+  --color-gray-700: #495057;
+  --color-gray-800: #343a40;
+  --color-gray-900: #212529;
+  --color-gray-000: #f8f9fa;
+
+  --font-sans:
+    "Pretendard Variable", Pretendard, -apple-system, BlinkMacSystemFont, system-ui, Roboto,
+    "Helvetica Neue", "Segoe UI", "Apple SD Gothic Neo", "Noto Sans KR", "Malgun Gothic",
+    "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", sans-serif;
+}
+
+/*
+  The default border color has changed to `currentcolor` in Tailwind CSS v4,
+  so we've added these compatibility styles to make sure everything still
+  looks the same as it did with Tailwind CSS v3.
+
+  If we ever want to remove these styles, we need to add an explicit border
+  color utility to any element that depends on these defaults.
+*/
+@layer base {
+  *,
+  ::after,
+  ::before,
+  ::backdrop,
+  ::file-selector-button {
+    border-color: var(--color-gray-200, currentcolor);
+  }
+}