Fix ThemePage activateColorScheme prop type

Prop was typed with 'unknown' parameters, which TypeScript rejected when
assigned the narrower signature from useIframeManager. Replace with the
canonical DesignSpecThemeSelector from schema and drop the duplicate
SelectorLike alias in the iframe manager.

Author: kurtstohrer

src/shell/components/ThemePage.vue

@@ -3,7 +3,7 @@ import { ref, computed, watch, type Ref, type MaybeRef, toRef } from 'vue'
 import { useDesignSpec } from '../composables/useDesignSpec'
 import { useThemePreview } from '../composables/useThemePreview'
 import { useTasks } from '../composables/useTasks'
-import type { DesignSpecToken, DesignSpecTheme, ColorSchemeInfo } from '../../schema'
+import type { DesignSpecToken, DesignSpecTheme, DesignSpecThemeSelector, ColorSchemeInfo } from '../../schema'
 import type { ColorSchemeResult } from '../../shared/bridge-types'
 import ColorPalettePicker from './ColorPalettePicker.vue'
 import ThemeLibrariesTab from './ThemeLibrariesTab.vue'
@@ -21,7 +21,7 @@ const props = defineProps<{
    * the app actually switches — without this, clicking only pins the edit
    * target and the user has to toggle the app manually to preview.
    */
-  activateColorScheme?: (selector: unknown, all: unknown[]) => Promise<void>
+  activateColorScheme?: (selector: DesignSpecThemeSelector | null | undefined, all?: DesignSpecThemeSelector[]) => Promise<void>
 }>()
 
 const { designSpec, isInitialized, isLoading } = useDesignSpec()

src/shell/composables/useIframeManager.ts

@@ -13,6 +13,7 @@ import type {
   ComputeAccessibilityInfoResult, AccessibilityInfo,
   ComputeTabOrderResult, TabOrderEntry,
 } from '../../shared/bridge-types'
+import type { DesignSpecThemeSelector } from '../../schema'
 
 export function useIframeManager(iframeRef: Ref<HTMLIFrameElement | null>) {
   const currentRoute = ref('/')
@@ -363,15 +364,9 @@ export function useIframeManager(iframeRef: Ref<HTMLIFrameElement | null>) {
    * 'color-scheme:changed' push which seeds `colorScheme` — but we also set it
    * optimistically so the UI updates without a round-trip.
    */
-  type SelectorLike = {
-    kind: 'attribute' | 'class' | 'media' | 'default'
-    host?: 'html' | 'body'
-    name?: string
-    value?: string
-  }
   async function activateColorScheme(
-    selector: SelectorLike | null | undefined,
-    all: SelectorLike[] = []
+    selector: DesignSpecThemeSelector | null | undefined,
+    all: DesignSpecThemeSelector[] = []
   ): Promise<void> {
     const iframe = iframeRef.value
     const doc = iframe?.contentDocument