feat: add multiselect field type to x-oap-ui-config system

[Concept-Vi]

Summary

Adds generic multiselect field type to OAP's x-oap-ui-config system, enabling any agent to use List[str] configuration fields with multiselect UI.

Changes

• Type Definitions: Add "multiselect" to ConfigurableFieldUIType union and define ConfigurableFieldMultiselectMetadata interface
• Component: Create MultiselectCombobox component (generalized from AgentsCombobox)
• Utility: Add deepEqual for array comparison in visible_if conditions
• Integration: Wire multiselect into ConfigField rendering
• Tests: Unit tests for component, utility, and visible_if integration
• Documentation: Usage guide for Python backend and frontend

Testing

• Unit tests pass (component, utility, visible_if)
• Integration tests pass
• E2E manual testing completed
• Type checking passes
• Linting passes
• Build succeeds

Usage Example

output_formats: List[str] = Field(
    default=["markdown", "json"],
    metadata={
        "x_oap_ui_config": {
            "type": "multiselect",
            "options": [
                {"label": "Markdown", "value": "markdown"},
                {"label": "JSON", "value": "json"}
            ]
        }
    }
)

Dependencies

All dependencies already present (Radix UI, cmdk, TypeScript).

Backward Compatibility

Fully backward compatible - existing configs work unchanged.

Estimated Review Time

~30 minutes

[vercel]

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