design: change to minimalistic and clean light theme

- Replace Matrix/terminal dark theme with modern light design
- Update Tailwind config with clean, professional color palette
- Change from monospace to Inter sans-serif font
- Update chart styling to use white background with subtle grids
- Remove glow effects and neon colors from buttons and UI
- Update color picker with better color options
- Improve sidebar spacing and typography
- Update annotation badges with softer colors
- Change scrollbar styling to match light theme

src/components/FileUpload.tsx

@@ -58,8 +58,8 @@ export default function FileUpload({ onUploadSuccess }: FileUploadProps) {
   };
 
   return (
-    <div className="mb-4 p-4 bg-secondary/50 rounded-lg border border-border">
-      <h3 className="text-sm font-semibold mb-2">Upload CSV Data</h3>
+    <div className="p-4 bg-muted rounded-lg border border-border">
+      <h3 className="text-sm font-medium mb-3 text-foreground">Upload CSV Data</h3>
 
       <input
         ref={fileInputRef}
@@ -73,7 +73,6 @@ export default function FileUpload({ onUploadSuccess }: FileUploadProps) {
 
       <Button
         variant="outline"
-        size="sm"
         className="w-full"
         onClick={() => fileInputRef.current?.click()}
         disabled={isUploading}
@@ -84,10 +83,10 @@ export default function FileUpload({ onUploadSuccess }: FileUploadProps) {
 
       {message && (
         <div
-          className={`mt-2 text-xs p-2 rounded ${
+          className={`mt-3 text-xs p-3 rounded-md ${
             message.type === 'success'
-              ? 'bg-green-500/10 text-green-500 border border-green-500/20'
-              : 'bg-red-500/10 text-red-500 border border-red-500/20'
+              ? 'bg-emerald-50 text-emerald-700 border border-emerald-200'
+              : 'bg-red-50 text-red-700 border border-red-200'
           }`}
         >
           {message.text}