feat: add element-inspector

- Implemented Rulers component for zoom/pan-aware rulers on canvas.
- Created Stage component to serve as a zoomable and pannable viewport for the device frame.
- Developed Toolbar component for responsive controls, including device presets and zoom functionalities.
- Introduced useFrame composable to manage iframe interactions and inspections.
- Established a reactive store to manage application state, including guides and viewport dimensions.
- Added utility functions for color parsing and box model calculations.
- Integrated Tailwind CSS for styling and improved scrollbar aesthetics.
- Implemented unit tests for color utilities and rectangle calculations.
- Configured TypeScript and Vite for the project setup.

element-inspector/src/ui/styles/style.css

@@ -0,0 +1,23 @@
+@import 'tailwindcss';
+
+/* Scan the JSX components for utility classes. */
+@source '../../**/*.{ts,tsx}';
+
+/* Dotted canvas background for the stage. */
+@layer components {
+  .ei-grid {
+    background-color: #0b0e14;
+    background-image: radial-gradient(circle, rgba(148, 163, 184, 0.12) 1px, transparent 1px);
+    background-size: 16px 16px;
+  }
+}
+
+/* Compact scrollbars inside the overlay. */
+.ei-root *::-webkit-scrollbar {
+  width: 10px;
+  height: 10px;
+}
+.ei-root *::-webkit-scrollbar-thumb {
+  background: rgba(148, 163, 184, 0.25);
+  border-radius: 6px;
+}