Add ability for internal users to rename models in Language Models editor

[Copilot]

Adds a rename icon next to the visibility icon in the Language Models editor for internal users (github/microsoft/ms-copilot/MicrosoftCopilot org members).

Changes

• ILanguageModelsService interface: Added updateModelDisplayName() and getModelDisplayName() methods
• LanguageModelsService: Persist custom model names to profile storage (chatModelDisplayNames), apply custom names in lookupLanguageModel()
• GutterColumnRenderer: Show edit icon for internal users via chatEntitlementService.isInternal, opens quick input dialog
• CSS: Always show rename icon when model has custom name (not just on hover)
• Tests: Added rename tests, updated mock/null service implementations

UI Behavior

• Internal users see an edit (✏️) icon next to visibility (👁️) on model row hover
• Clicking opens input dialog to set custom display name
• Custom names persist across sessions and display throughout the UI
• Gutter column widens from 40px → 64px for internal users to fit both icons

Original prompt

Add ability for internal users to rename models that show in the UI from Chat: Manage Language Models command in the Language Models editor. Today, there is no way to rename a model. Add the ability to rename a model with a new icon in the same location as the visibility icon.

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