feat: add header components and version switcher for docs

docs/composables/useVersions.ts

@@ -0,0 +1,60 @@
+interface Version {
+    version: string
+    title: string
+    path: string
+    branch: string
+    isLatest: boolean
+}
+
+const versions = ref<Version[]>([])
+const isLoaded = ref(false)
+const isLoading = ref(false)
+
+export function useVersions() {
+    const config = useRuntimeConfig()
+    const currentVersion = config.public.docsVersion || '1.x'
+
+    async function loadVersions() {
+        if (isLoaded.value || isLoading.value) return
+        isLoading.value = true
+
+        try {
+            const res = await fetch('/comments/versions.json')
+            if (res.ok) {
+                versions.value = await res.json()
+            }
+        } catch (e) {
+            console.warn('Failed to load versions.json:', e)
+        } finally {
+            isLoaded.value = true
+            isLoading.value = false
+        }
+    }
+
+    const latestVersion = computed(() =>
+        versions.value.find(v => v.isLatest)
+    )
+
+    const currentVersionInfo = computed(() =>
+        versions.value.find(v => v.version === currentVersion)
+    )
+
+    const isOldVersion = computed(() => {
+        if (!isLoaded.value) return false
+        return currentVersionInfo.value?.isLatest === false
+    })
+
+    const currentTitle = computed(() =>
+        currentVersionInfo.value?.title || currentVersion
+    )
+
+    return {
+        versions,
+        currentVersion,
+        currentTitle,
+        latestVersion,
+        isOldVersion,
+        isLoaded,
+        loadVersions,
+    }
+}