Fix license activation and plugin requests ignoring proxy settings

Make yaak_api_client() read proxy settings from the database and apply
them to the reqwest client. Also replace bare reqwest::Client::new()
calls in license activate/deactivate with yaak_api_client() so they
get proxy support (and consistent UA/headers/timeout).

Fixes https://yaak.app/feedback/posts/cannot-activate-license

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates-tauri/yaak-tauri-utils/Cargo.toml

@@ -11,3 +11,5 @@ thiserror = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 regex = "1.11.0"
 yaak-common = { workspace = true }
+yaak-models = { workspace = true }
+log = { workspace = true }