style: restore original color scheme to shadcn/ui components

Restore the vibrant color palette from the pre-refactoring version while
maintaining shadcn/ui component architecture and modern design patterns.

## Color Scheme Restoration

### Button Component
- **default variant**: Blue primary (`bg-blue-500`) - matches old `primary`
- **destructive variant**: Red (`bg-red-500`) - matches old `danger`
- **secondary variant**: Gray text (`text-gray-500`) - matches old `secondary`
- **ghost variant**: Transparent hover (`hover:bg-gray-100`) - matches old `ghost`
- **mcp variant**: Emerald green (`bg-emerald-500`) - matches old `mcp`
- Updated border-radius to `rounded-lg` for consistency

### CSS Variables
- Set `--primary` to blue (`hsl(217 91% 60%)` ≈ `bg-blue-500`)
- Added complete shadcn/ui theme variables for light/dark modes
- Maintained semantic color tokens for maintainability

### Component-Specific Colors
- **"Currently Using" badge**: Green (`bg-green-500/10 text-green-500`)
- **Delete button hover**: Red (`hover:text-red-500 hover:bg-red-100`)
- **MCP button**: Emerald green with minimum width (`min-w-[80px]`)
- **Links/URLs**: Blue (`text-blue-500`)

## Benefits

- ✅ Restored original vibrant UI (blue, green, red accents)
- ✅ Maintained shadcn/ui component system (accessibility, animations)
- ✅ Easy global theming via CSS variables
- ✅ Consistent design language across all components
- ✅ Code formatted with Prettier (shadcn/ui standards)

## Files Changed

- `src/index.css`: Added shadcn/ui theme variables with blue primary
- `src/components/ui/button.tsx`: Restored all original button color variants
- `src/components/providers/ProviderCard.tsx`: Green badge for current provider
- `src/components/providers/ProviderActions.tsx`: Red hover for delete button
- `src/components/mcp/McpPanel.tsx`: Use `mcp` variant for consistency
- `src/App.tsx`: MCP button with emerald color and wider width

The UI now matches the original colorful design while leveraging modern
shadcn/ui components for better maintainability and user experience.

src/components/providers/EditProviderDialog.tsx

@@ -45,9 +45,7 @@ export function EditProviderDialog({
         name: values.name.trim(),
         websiteUrl: values.websiteUrl?.trim() || undefined,
         settingsConfig: parsedConfig,
-        ...(values.presetCategory
-          ? { category: values.presetCategory }
-          : {}),
+        ...(values.presetCategory ? { category: values.presetCategory } : {}),
       };
 
       await onSubmit(updatedProvider);

src/components/providers/ProviderActions.tsx

@@ -64,8 +64,9 @@ export function ProviderActions({
         onClick={onDelete}
         disabled={isCurrent}
         className={cn(
-          "text-destructive hover:text-destructive",
-          isCurrent && "text-muted-foreground hover:text-muted-foreground",
+          "hover:text-red-500 hover:bg-red-100 dark:hover:text-red-400 dark:hover:bg-red-500/10",
+          isCurrent &&
+            "text-muted-foreground hover:text-muted-foreground hover:bg-transparent",
         )}
       >
         <Trash2 className="h-4 w-4" />

src/components/providers/ProviderCard.tsx

@@ -117,7 +117,7 @@ export function ProviderCard({
                 {provider.name}
               </h3>
               {isCurrent && (
-                <span className="rounded-full bg-primary/10 px-2 py-0.5 text-xs font-medium text-primary">
+                <span className="rounded-full bg-green-500/10 px-2 py-0.5 text-xs font-medium text-green-500 dark:text-green-400">
                   {t("provider.currentlyUsing", { defaultValue: "当前使用" })}
                 </span>
               )}

src/components/providers/forms/ProviderForm.tsx

@@ -26,10 +26,7 @@ import JsonEditor from "@/components/JsonEditor";
 import { providerSchema, type ProviderFormData } from "@/lib/schemas/provider";
 import type { AppType } from "@/lib/api";
 import type { ProviderCategory } from "@/types";
-import {
-  providerPresets,
-  type ProviderPreset,
-} from "@/config/providerPresets";
+import { providerPresets, type ProviderPreset } from "@/config/providerPresets";
 import {
   codexProviderPresets,
   type CodexProviderPreset,
@@ -37,11 +34,7 @@ import {
 import { applyTemplateValues } from "@/utils/providerConfigUtils";
 
 const CLAUDE_DEFAULT_CONFIG = JSON.stringify({ env: {}, config: {} }, null, 2);
-const CODEX_DEFAULT_CONFIG = JSON.stringify(
-  { auth: {}, config: "" },
-  null,
-  2,
-);
+const CODEX_DEFAULT_CONFIG = JSON.stringify({ auth: {}, config: "" }, null, 2);
 
 type PresetEntry = {
   id: string;