feat: add class-variance-authority for card styling and enhance color palettes

- Introduced `class-variance-authority` to manage card component styles, allowing for flexible variant and layout options.
- Added a new color palette for "Fire" to the CSS for improved theming.
- Updated `Card` and `PostCard` components to utilize the new styling system, enhancing visual consistency and responsiveness.
- Refined layout and styling in various components for better user experience.

src/app.css

@@ -51,6 +51,19 @@
   --color-himmel-800: #1a2c36;
   --color-himmel-900: #0e181e;
 
+  /* Palette: Fire (Tertiary) */
+  --color-fire-50: #fdf2f1;
+  --color-fire-100: #fbe5e3;
+  --color-fire-200: #f7c9c5;
+  --color-fire-300: #f2a8a2;
+  --color-fire-400: #eb8078;
+  --color-fire-500: #e35651;
+  --color-fire-600: #d93d36;
+  --color-fire-700: #c82e27;
+  --color-fire-800: #b5231e;
+  --color-fire-900: #981b18;
+  --color-fire-950: #5d0f0b;
+
   /* Palette: Stein (Neutrals) */
   --color-stein-0: #ffffff;
   --color-stein-50: #f7f8f7;