Hide manage model picker action item when required

[DonJayamanne]

No description provided.

[Copilot]

Pull request overview

This PR adds a canManageModels parameter to conditionally control the visibility of the "Manage Models..." action item in the chat model picker. This allows the model picker to hide the management option when used in specific contexts, such as sessions with specialized model requirements (indicated by getCurrentSessionType()).

Changes:

• Added canManageModels: boolean parameter to buildModelPickerItems function
• Modified conditional logic to check canManageModels before displaying the "Manage Models..." entry and its preceding separator
• Updated all test call sites and added comprehensive test coverage for the new functionality

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/vs/workbench/contrib/chat/browser/widget/input/chatModelPicker.ts	Added canManageModels parameter to buildModelPickerItems function and updated conditional logic to respect this flag when showing the "Manage Models..." action
src/vs/workbench/contrib/chat/test/browser/widget/input/chatModelPicker.test.ts	Updated test helper function to accept canManageModels option, added 6 new tests covering various scenarios, and updated existing direct call sites to pass true explicitly