fix(demo): harden cross-platform demo imports

Rebase official Demo timelines against the browser timezone, bound stalled downloads, and roll back partial batches across Desktop, CLI Web, and Web WASM. Document the platform cleanup hook's established best-effort boundary.

apps/cli/src/http/routes/web/import.ts

@@ -407,8 +407,9 @@ export function registerImportRoutes(
 
   // ==================== Demo Import ====================
 
-  server.post<{ Body: { locale?: string } }>('/_web/demo/import', async (request, reply) => {
-    const locale = (request.body as any)?.locale === 'cn' ? 'cn' : 'en'
+  server.post<{ Body: { locale?: string; timeZone?: string } }>('/_web/demo/import', async (request, reply) => {
+    const locale = request.body?.locale === 'cn' ? 'cn' : 'en'
+    const targetTimeZone = typeof request.body?.timeZone === 'string' ? request.body.timeZone : undefined
     const nativeBinding = resolveNativeBinding()
 
     reply.raw.writeHead(200, {
@@ -424,7 +425,11 @@ export function registerImportRoutes(
     const result = await importDemoSessions({
       locale,
       tempPrefix: 'cli-demo-',
+      targetTimeZone,
       importFile: (filePath) => streamImport(dbManager, filePath, { nativeBinding }),
+      deleteSession: (sessionId) => {
+        dbManager.deleteSessionDatabaseFiles(sessionId)
+      },
       onProgress: (progress) => sendEvent('progress', progress),
     })
     sendEvent('result', result)