feat/agent-model-select-type

[ultrahighsuper]

Related Issue

Description

In the Add Agent dialog (Advanced Model Configuration), the Model Type field was a free-text input, which made it easy to mistype and inconsistent with the rest of the UI.

This change updates src/components/AddWorker/index.tsx so Model Type is a Select dropdown:

• Disabled until a Model Platform is selected.
• Shows suggested model IDs based on platform.
• Provides a Custom Model option (only then shows a secondary input for manual entry).

Testing Evidence (REQUIRED)

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

[ultrahighsuper]

@4pmtong
Please check this PR.

[ultrahighsuper]

@Wendong-Fan
please check this PR.
It has 2 weeks pending.