feat(web): implement demo import for web mode via SSE endpoint

- Add POST /_web/demo/import backend endpoint: downloads demo data from
  chatlab.fun and imports using streamImport with SSE progress
- Refactor DemoImportButton.vue to support both Electron (IPC) and
  Web (SSE fetch) modes with shared result handling

packages/server/src/http/routes/web.ts

@@ -470,6 +470,83 @@ export function registerWebRoutes(server: FastifyInstance, dbManager: DatabaseMa
     return { success: true }
   })
 
+  // ==================== Demo 示例数据 ====================
+
+  const DEMO_BASE_URL = 'https://chatlab.fun/assets/demo'
+
+  server.post<{ Body: { locale?: string } }>('/_web/demo/import', async (request, reply) => {
+    const locale = (request.body as any)?.locale || 'en'
+    const nativeBinding = resolveNativeBinding()
+
+    reply.raw.writeHead(200, {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      Connection: 'keep-alive',
+    })
+
+    function sendEvent(event: string, data: unknown) {
+      reply.raw.write(`event: ${event}\ndata: ${JSON.stringify(data)}\n\n`)
+    }
+
+    const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'chatlab-demo-'))
+    const groupPath = path.join(tmpDir, 'demo-group.json')
+    const privatePath = path.join(tmpDir, 'demo-private.json')
+
+    try {
+      sendEvent('progress', { stage: 'downloading', current: 1, total: 2 })
+      const groupResp = await fetch(`${DEMO_BASE_URL}/${locale}/demo-group.json`, {
+        signal: AbortSignal.timeout(60_000),
+      })
+      if (!groupResp.ok) throw new Error(`Download group demo failed: ${groupResp.status}`)
+      fs.writeFileSync(groupPath, Buffer.from(await groupResp.arrayBuffer()))
+
+      sendEvent('progress', { stage: 'downloading', current: 2, total: 2 })
+      const privateResp = await fetch(`${DEMO_BASE_URL}/${locale}/demo-private.json`, {
+        signal: AbortSignal.timeout(60_000),
+      })
+      if (!privateResp.ok) throw new Error(`Download private demo failed: ${privateResp.status}`)
+      fs.writeFileSync(privatePath, Buffer.from(await privateResp.arrayBuffer()))
+
+      sendEvent('progress', { stage: 'importing', current: 1, total: 2 })
+      const groupResult = await streamImport(dbManager, groupPath, { nativeBinding })
+
+      if (!groupResult.success) throw new Error(groupResult.error || 'Failed to import group demo')
+
+      sendEvent('progress', { stage: 'importing', current: 2, total: 2 })
+      const privateResult = await streamImport(dbManager, privatePath, { nativeBinding })
+
+      if (!privateResult.success) throw new Error(privateResult.error || 'Failed to import private demo')
+
+      sendEvent('progress', { stage: 'done', current: 2, total: 2 })
+      sendEvent('result', {
+        success: true,
+        groupSessionId: groupResult.sessionId,
+        privateSessionId: privateResult.sessionId,
+      })
+    } catch (err) {
+      const message = err instanceof Error ? err.message : String(err)
+      sendEvent('progress', { stage: 'error', current: 0, total: 2, message })
+      sendEvent('result', { success: false, error: message })
+    } finally {
+      try {
+        fs.unlinkSync(groupPath)
+      } catch {
+        /* ignore */
+      }
+      try {
+        fs.unlinkSync(privatePath)
+      } catch {
+        /* ignore */
+      }
+      try {
+        fs.rmdirSync(tmpDir)
+      } catch {
+        /* ignore */
+      }
+      reply.raw.end()
+    }
+  })
+
   // ==================== 导入管线 ====================
 
   server.get('/_web/supported-formats', async () => {

src/pages/home/components/DemoImportButton.vue

@@ -25,26 +25,83 @@ async function navigateToSession(sessionId: string) {
   }
 }
 
-async function handleImport() {
-  if (!IS_ELECTRON) {
-    error.value = t('home.demo.notAvailableInWeb', 'Demo 导入功能暂仅在桌面端可用')
-    return
-  }
-
-  isImporting.value = true
-  error.value = null
-  stage.value = 'downloading'
-
+async function handleImportElectron() {
   const unsubscribe = window.chatApi.onDemoProgress((progress) => {
     if (progress.stage === 'downloading' || progress.stage === 'importing') {
       stage.value = progress.stage
     }
   })
 
+  const demoLocale = getChatlabSiteLocalePath(settingsStore.locale) || 'en'
+  const result = await window.chatApi.importDemo(demoLocale)
+  unsubscribe()
+  return result
+}
+
+async function handleImportWeb(): Promise<{
+  success: boolean
+  groupSessionId?: string
+  privateSessionId?: string
+  error?: string
+}> {
+  const demoLocale = getChatlabSiteLocalePath(settingsStore.locale) || 'en'
+
+  return new Promise((resolve) => {
+    const ctrl = new AbortController()
+    fetch('/_web/demo/import', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ locale: demoLocale }),
+      signal: ctrl.signal,
+    })
+      .then(async (resp) => {
+        if (!resp.ok || !resp.body) {
+          resolve({ success: false, error: `HTTP ${resp.status}` })
+          return
+        }
+
+        const reader = resp.body.getReader()
+        const decoder = new TextDecoder()
+        let buffer = ''
+
+        while (true) {
+          const { done, value } = await reader.read()
+          if (done) break
+          buffer += decoder.decode(value, { stream: true })
+
+          const lines = buffer.split('\n')
+          buffer = lines.pop() || ''
+
+          let eventType = ''
+          for (const line of lines) {
+            if (line.startsWith('event: ')) {
+              eventType = line.slice(7)
+            } else if (line.startsWith('data: ')) {
+              const data = JSON.parse(line.slice(6))
+              if (eventType === 'progress') {
+                if (data.stage === 'downloading' || data.stage === 'importing') {
+                  stage.value = data.stage
+                }
+              } else if (eventType === 'result') {
+                resolve(data)
+                return
+              }
+            }
+          }
+        }
+        resolve({ success: false, error: 'Stream ended without result' })
+      })
+      .catch((e) => resolve({ success: false, error: String(e) }))
+  })
+}
+
+async function handleImport() {
+  isImporting.value = true
+  error.value = null
+  stage.value = 'downloading'
+
   try {
-    const demoLocale = getChatlabSiteLocalePath(settingsStore.locale) || 'en'
-    const result = await window.chatApi.importDemo(demoLocale)
-    unsubscribe()
+    const result = IS_ELECTRON ? await handleImportElectron() : await handleImportWeb()
 
     if (result.success && result.groupSessionId) {
       await sessionStore.loadSessions()