Narrow component prop types, remove unused props and dead code (#2838)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

shared/ui/Payment.astro

@@ -1,8 +1,11 @@
 ---
+import type { AvatarSize } from './Avatar.astro'
+
 interface Props {
   payment?: string
   dark?: boolean
-  size?: string
+  /** core/scss/_variables.scss `$payment-sizes` (aliased to `$avatar-sizes`) */
+  size?: AvatarSize | undefined
   class?: string
   label?: string | undefined
 }