fix: resolve TypeScript compilation errors

Fixes:
- VideoPlayer.vue: restore allTags, filteredMarks, marksByTag (removed by mistake)
- PeopleView.vue: fix frameTime scope in playFaceDetailVideo catch block
- Both errors caused white screen on build failure

Root cause:
1. visibleTags duplicate declaration (old + new logic)
2. frameTime undefined in catch block (scope issue)

Solution:
1. Keep allTags/filteredMarks/marksByTag (needed in template)
2. Keep visibleTags (new logic for processor toggles)
3. Move frameTime calculation to correct scope in catch block

src/composables/useTheme.ts

@@ -0,0 +1,12 @@
+import { useDark, useToggle } from '@vueuse/core'
+
+export const isDark = useDark({
+  selector: 'html',
+  attribute: 'data-theme',
+  valueDark: 'dark',
+  valueLight: 'light',
+})
+
+export const toggleDark = () => {
+  isDark.value = !isDark.value
+}

src/composables/useZIndex.ts

@@ -0,0 +1,35 @@
+import { ref, computed } from 'vue'
+
+let baseZIndex = 10000
+const stack = ref<string[]>([])
+
+export function useZIndex() {
+  const push = (id: string): number => {
+    if (!stack.value.includes(id)) {
+      stack.value.push(id)
+    }
+    return baseZIndex + stack.value.indexOf(id) * 10
+  }
+
+  const pop = (id: string) => {
+    const idx = stack.value.indexOf(id)
+    if (idx >= 0) {
+      stack.value.splice(idx, 1)
+    }
+  }
+
+  const current = computed(() => baseZIndex + stack.value.length * 10)
+
+  return { push, pop, current }
+}
+
+let globalZIndex = 10000
+
+export function getNextZIndex(): number {
+  globalZIndex += 10
+  return globalZIndex
+}
+
+export function resetZIndex() {
+  globalZIndex = 10000
+}