feat: implement core UI components and build initial dashboard layout with navigation structure

src/components/ui/Select.jsx

@@ -0,0 +1,42 @@
+import React from 'react';
+
+const Select = React.forwardRef(({ label, error, options, className = '', ...props }, ref) => {
+  return (
+    <div className={`flex flex-col gap-1 ${className}`}>
+      {label && (
+        <label className="text-[var(--t-small)] font-medium text-fg-muted">
+          {label}
+        </label>
+      )}
+      <select
+        ref={ref}
+        className={`
+          w-full px-4 py-2.5 bg-paper border border-bg-warm rounded-[var(--r-sm)]
+          text-fg focus:outline-none focus:ring-2 focus:ring-accent focus:border-transparent
+          transition-all cursor-pointer appearance-none
+          ${error ? 'border-red-500 focus:ring-red-500' : ''}
+        `}
+        style={{
+          backgroundImage: `url("data:image/svg+xml;charset=UTF-8,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='currentColor' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3e%3cpolyline points='6 9 12 15 18 9'%3e%3c/polyline%3e%3c/svg%3e")`,
+          backgroundRepeat: 'no-repeat',
+          backgroundPosition: 'right 1rem center',
+          backgroundSize: '1em'
+        }}
+        {...props}
+      >
+        {options.map((opt) => (
+          <option key={opt.value} value={opt.value}>
+            {opt.label}
+          </option>
+        ))}
+      </select>
+      {error && (
+        <span className="text-xs text-red-500 mt-1">{error}</span>
+      )}
+    </div>
+  );
+});
+
+Select.displayName = 'Select';
+
+export default Select;