feat(ui): add SelectField renderer to InspectorPane for enum-constrained strings

[staging-devin-ai-integration]

Summary

The InspectorPane currently renders enum-constrained string properties as plain text inputs (StringField). After the select control type was added to Stream View overlay controls (PR #327), there is a UI inconsistency:

• Stream View (overlay controls): enum strings render as <select> dropdowns
• Inspector/Monitor View: enum strings render as free-text <input> fields

Proposed Solution

Add a SelectField renderer in InspectorPane.tsx that renders a dropdown when a tunable string property has an enum constraint in its JSON Schema. The field should:

1. Render a <select> dropdown with the enum values as options
2. Send an UpdateParams message on selection change
3. Follow the existing field renderer pattern (StringField, NumberField, BooleanField)

Context

• Found via Devin Review on PR feat(plugins/servo,ui): viewport scaling, compositor hints, select controls, graceful shutdown #327
• The schemaToControlConfigs utility in jsonSchema.ts already correctly maps enum strings to select controls — the gap is only in the Inspector view's direct field rendering.