Build Model Provider configuration tab

[itdove]

Description

Create Model Provider tab for configuring alternative AI models (Vertex AI, llama.cpp, etc).

Tasks

• Create ModelProviderTab component
• Implement profile DataList with add/edit/delete
• Create AddEditProfileModal with template selection
• Add form fields per provider type (dynamic)
• Implement profile validation
• Add cost calculator (optional)
• Show active profile indicator
• Handle enterprise/team enforcement (read-only mode)

Acceptance Criteria

• Profiles displayed in DataList
• Add/Edit/Delete profile buttons work
• Template selection (Vertex AI, llama.cpp, OpenRouter)
• Form fields adapt to selected template
• Active profile is visually distinct
• Enterprise enforcement shows warning + disables editing
• Validation prevents invalid configs
• Changes update parent state

Estimated Effort: 5-7 days

[itdove]

Child of #305