feat: add source identifier to API requests for telemetry

[irisyann]

This PR introduces a source=cli query parameter to all outbound API requests made by the CLI.

💡 Rationale

To ensure the long-term stability and performance of our API services, we need better visibility into how different clients interact with our infrastructure. Adding this identifier allows our backend to:

• Monitor Performance: Distinguish CLI-specific traffic to identify and resolve latency issues or errors unique to this client.
• Optimize Resources: Understand aggregate usage patterns to better scale our infrastructure and ensure a reliable experience for all users.
• Improve Developer Experience: Use high-level metrics to prioritize features and optimizations that benefit CLI users most.

🛠️ Changes

• Updated the internal API client to append source=cli to request URLs.
• Logic accounts for existing query parameters to ensure URL formatting remains valid.