feat: add automatic update functionality for Electron app

Closes #613

- Add electron-updater for Windows NSIS and Linux AppImage auto-update
- macOS and Linux DEB fall back to GitHub API check with download link
- Add "Check for Updates" menu item with i18n (en, zh, ja, zh-Hant)
- Fix Windows CI workflow to publish correct latest.yml after code signing
- Add update toast notifications in renderer via sonner

hooks/use-auto-update.ts

@@ -0,0 +1,86 @@
+import { createElement, useEffect, useRef } from "react"
+import { toast } from "sonner"
+import { UpdateToast } from "@/components/update-toast"
+
+export function useAutoUpdate() {
+    const downloadToastId = useRef<string | number | null>(null)
+
+    useEffect(() => {
+        const api = (window as Window).electronAPI
+        if (!api?.onUpdateStatus) return
+
+        const cleanup = api.onUpdateStatus((data) => {
+            switch (data.status) {
+                case "available":
+                    toast.custom(
+                        (t) =>
+                            createElement(UpdateToast, {
+                                variant: "download",
+                                version: data.version,
+                                onDownload: () => {
+                                    toast.dismiss(t)
+                                    api.startDownload().catch(() => {
+                                        // Error will come through update-status channel
+                                    })
+                                },
+                                onDismiss: () => toast.dismiss(t),
+                            }),
+                        { duration: 15000 },
+                    )
+                    break
+
+                case "available-manual":
+                    toast.custom(
+                        (t) =>
+                            createElement(UpdateToast, {
+                                variant: "manual",
+                                version: data.version,
+                                url: data.url,
+                                onDismiss: () => toast.dismiss(t),
+                            }),
+                        { duration: Number.POSITIVE_INFINITY },
+                    )
+                    break
+
+                case "downloading": {
+                    const id =
+                        downloadToastId.current ??
+                        `download-progress-${Date.now()}`
+                    downloadToastId.current = id
+                    toast.custom(
+                        (t) =>
+                            createElement(UpdateToast, {
+                                variant: "downloading",
+                                percent: data.percent,
+                                onDismiss: () => toast.dismiss(t),
+                            }),
+                        { id, duration: Number.POSITIVE_INFINITY },
+                    )
+                    break
+                }
+
+                case "downloaded":
+                    // Dismiss progress toast — native restart dialog handles the rest
+                    if (downloadToastId.current) {
+                        toast.dismiss(downloadToastId.current)
+                        downloadToastId.current = null
+                    }
+                    break
+
+                case "error":
+                    if (downloadToastId.current) {
+                        // Error during active download — inform the user
+                        toast.dismiss(downloadToastId.current)
+                        downloadToastId.current = null
+                        toast.error(
+                            "Update download failed. Please try again later.",
+                        )
+                    }
+                    // Otherwise: silent — background check failure, logged in main process
+                    break
+            }
+        })
+
+        return cleanup
+    }, [])
+}