SurfaceSlotCategory

SurfaceSlotCategory = "fixed" | "gated" | "triggered"

Surface slot category that controls rendering behavior:

• fixed — Embedded in a page; always rendered inline when the user qualifies (e.g. a banner, an inline card, a quota meter).
• gated — Appears on button clicks or when a feature is attempted (e.g. a modal gate, a feature-lock prompt).
• triggered — Server-driven; rules are evaluated, user qualifies for a segment, and a surface template is rendered as a toast, modal, tooltip, etc.