fix: avoid overwriting manually edited provider models

[fancyboi999]

Summary

• keep user-entered model list when editing a provider
• only auto-sync models after save when the model list was not manually changed
• preserve existing auto-sync behavior for API key/base URL edits

Root Cause

When editing a provider, save flow always triggered syncProviderModels, which replaces provider.model with remote fetched models. This overwrote manual model edits immediately after saving.

Verification

• npx electron-vite build passed
• confirmed save flow now skips auto-sync when model list changed manually

Closes #2

[fancyboi999]

补充回归验证（2026-02-27，本地 mac）：

1. 打开设置 -> 编辑 memefast 供应商
2. 填入 API Key：dummy-key-issue2
3. 将模型改为：my-model-a, my-model-b
4. 点击保存后重新打开编辑弹窗，读取输入值

结果：模型值保持为 my-model-a, my-model-b，未被自动同步覆盖。

另外验证：仅改名称保存时，不影响该修复路径（不会把手动模型改回默认）。