feat: integrate Codex common config snippet and template modal features

- Created useCodexCommonConfig hook for managing Codex TOML common config
- Persists to localStorage with key 'cc-switch:codex-common-config-snippet'
- Added isCodexTemplateModalOpen state to ProviderForm
- Connected all CodexConfigEditor props:
  - Common config snippet management (useCommonConfig, handlers)
  - Template modal state (isTemplateModalOpen, setIsTemplateModalOpen)
  - Form field callbacks (onWebsiteUrlChange, onNameChange)
  - Custom mode detection (isCustomMode)
- Hook structure mirrors useCommonConfigSnippet for consistency

src/components/providers/forms/hooks/index.ts

@@ -8,3 +8,4 @@ export { useCustomEndpoints } from "./useCustomEndpoints";
 export { useKimiModelSelector } from "./useKimiModelSelector";
 export { useTemplateValues } from "./useTemplateValues";
 export { useCommonConfigSnippet } from "./useCommonConfigSnippet";
+export { useCodexCommonConfig } from "./useCodexCommonConfig";