feat(sponsor): add PackyCode as official partner

- Add PackyCode to sponsor section in README (both EN/ZH)
- Add PackyCode logo to assets/partners/logos/
- Mark PackyCode as partner in provider presets (Claude & Codex)
- Add promotion message to i18n files with 10% discount info

src/config/claudeProviderPresets.ts

@@ -248,7 +248,7 @@ export const providerPresets: ProviderPreset[] = [
   {
     name: "PackyCode",
     websiteUrl: "https://www.packyapi.com",
-    apiKeyUrl: "https://www.packyapi.com",
+    apiKeyUrl: "https://www.packyapi.com/register?aff=cc-switch",
     settingsConfig: {
       env: {
         ANTHROPIC_BASE_URL: "https://www.packyapi.com",
@@ -261,6 +261,8 @@ export const providerPresets: ProviderPreset[] = [
       "https://api-slb.packyapi.com",
     ],
     category: "third_party",
+    isPartner: true, // 合作伙伴
+    partnerPromotionKey: "packycode", // 促销信息 i18n key
   },
   {
     name: "AnyRouter",