refactor: consolidate provider form components

This commit completes Stage 2.5-2.6 of the refactoring plan by:

- Consolidating 8 provider form files (1941+ lines) into a single
  unified ProviderForm component (353 lines), reducing code by ~82%
- Implementing modern form management with react-hook-form and zod
- Adding preset provider categorization with grouped select UI
- Supporting dual-mode operation for both Claude and Codex configs
- Removing redundant subcomponents:
  - ApiKeyInput.tsx (72 lines)
  - ClaudeConfigEditor.tsx (205 lines)
  - CodexConfigEditor.tsx (667 lines)
  - EndpointSpeedTest.tsx (636 lines)
  - KimiModelSelector.tsx (195 lines)
  - PresetSelector.tsx (119 lines)

Key improvements:
- Type-safe form values with ProviderFormValues extension
- Automatic template value application for presets
- Better internationalization coverage
- Cleaner separation of concerns
- Enhanced UX with categorized preset groups

Updates AddProviderDialog and EditProviderDialog to pass appType prop
and handle preset category metadata.

src/App.tsx

@@ -293,6 +293,7 @@ function App() {
           }
         }}
         onSubmit={handleEditProvider}
+        appType={activeApp}
       />
 
       {usageProvider && (