feat: add custom AI model support in selector

[souvikDevloper]

PR Description

This PR adds support for creating and appending a custom AI model from the AI Model Selector dialog.

Implemented changes:

• addNewModel now returns a Model
• empty model ID is rejected
• display name defaults to model ID when left blank
• the Add button in the AI Model Selector is wired and appends the new model to the currently selected provider
• added tests for validation, display-name fallback, and successful add flow

Demo: custom AI model add flow for #1315

API.Dash.2026-03-16.17-14-13.mp4

The demo shows:

1. Opening the AI Model Selector
2. Clicking the Add button
3. Rejecting empty model ID
4. Leaving display name blank so it falls back to the model ID
5. Successfully adding a custom model, seeing it appear immediately in the selected provider’s model list, selecting it, and saving it back to the AI request screen

Related Issues

• Closes Implement "Add Custom Model" functionality in AI Model Selector #1315
• Supersedes feat: add custom AI model support in selector #1339 (closed because demo video was missing)

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch (run flutter upgrade and verify)
• I have run the tests (flutter test) and all tests are passing

Added/updated tests?

We encourage you to add relevant test cases.

• Yes
• No, and this is why: please replace this line with details on why tests have not been included

Added tests:

• rejects empty model ID
• uses model ID as display name when blank
• successful add flow updates selector data/UI

Testing

• dart analyze lib/screens/common_widgets/ai/dialog_add_ai_model.dart lib/screens/common_widgets/ai/ai_model_selector_dialog.dart test/screens/common_widgets/ai/ai_model_selector_dialog_test.dart
• flutter test test/screens/common_widgets/ai/ai_model_selector_dialog_test.dart

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux

[souvikDevloper]

@animator as per your previous feedback i included the demo video please review the details and let me know your feedback!

[rafiamaqsood]

Hi @souvikDevloper , I’ve also been working on this issue and implemented a similar solution locally
I’ll review your PR and suggest improvements or help with testing if needed.

[souvikDevloper]

Hi @souvikDevloper , I’ve also been working on this issue and implemented a similar solution locally I’ll review your PR and suggest improvements or help with testing if needed.

fine let first maintainers @animator give feedback then we can split the work