feat(deeplink): add config file support for deeplink import

Support importing provider configuration from embedded or remote config files.
- Add base64 dependency for config content encoding
- Support config, configFormat, and configUrl parameters
- Make homepage/endpoint/apiKey optional when config is provided
- Add config parsing and merging logic

src-tauri/Cargo.lock

@@ -610,6 +610,7 @@ version = "3.7.0"
 dependencies = [
  "anyhow",
  "auto-launch",
+ "base64 0.22.1",
  "chrono",
  "dirs 5.0.1",
  "futures",