Before Submitting This PR

Please confirm you have done the following:

• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate
• I have read CONTRIBUTING.md

If this is a feature or change that was previously closed/rejected:

• I have explained in the description below why this should be reconsidered
• I have gathered community feedback (link to discussion below)

Human Written Description

I wanted to use Z.AI for transcript post-processing in Handy, but it was not available in the built-in provider list. This is available via the custom provider but I feel a native integration is easier. This change adds Z.AI as a default post-process provider using the standard OpenAI-compatible endpoint so users with a Z.AI plan can configure their API key and model directly in settings.

Related Issues/Discussions

Fixes #
Discussion: N/A

Community Feedback

No public discussion.

Testing

• cargo check --manifest-path src-tauri/Cargo.toml
• Manual verification of provider registration in src-tauri/src/settings.rs

Screenshots/Videos (if applicable)

AI Assistance

• No AI was used in this PR
• AI was used (please describe below)

If AI was used:

• Tools used: OpenCode (GPT-5.3-Codex)
• How extensively: Helped understanding the code, run checks, and prepare PR content.