fix(updater): surface download failures and dev-mode no-op in UI

Two symptoms collapsed into the same report: "click Download, button
disables briefly, re-enables, nothing happens."

1. In dev mode `app.isPackaged` is false and `downloadUpdate` silently
   returned a snapshot. The renderer saw no state change and gave up.
   Now we emit a state='error' with a human message explaining updates
   require a packaged build.

2. In prod, if electron-updater's `downloadUpdate()` rejects (network,
   signature check, missing platform yml), the catch set state='error'
   but never surfaced the error to the foreground toast. Now the
   renderer inspects the returned snapshot and toasts whatever error
   string came back.

3. Optimistically transition state → 'downloading' the moment
   downloadUpdate is called, and → 'ready' on promise resolution —
   some platforms race the `update-downloaded` event past our await.

Added main-side console.log around downloadUpdate so future reports
show what actually happened.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: beautyfree

src/main/app-updater.ts

@@ -157,10 +157,31 @@ export async function checkForUpdate(): Promise<AppUpdateStatusJson> {
 }
 
 export async function downloadUpdate(): Promise<AppUpdateStatusJson> {
-	if (!app.isPackaged) return snapshot();
+	// In dev the autoUpdater is a no-op — surface that as a clear error state
+	// so the UI shows something instead of the button silently re-enabling.
+	if (!app.isPackaged) {
+		lastError =
+			"Updates only work in a packaged build (bun run dist:mac / :win / :linux).";
+		setState("error");
+		return snapshot();
+	}
+	console.log("[updater] downloadUpdate() invoked; state=", state);
+	// Optimistic transition so the renderer UI reflects work-in-progress even
+	// before the first `download-progress` event fires (those can lag 2–3s on
+	// slow networks).
+	setState("downloading");
 	try {
-		await autoUpdater.downloadUpdate();
+		const result = await autoUpdater.downloadUpdate();
+		console.log("[updater] downloadUpdate() resolved with:", result);
+		// If update-downloaded event didn't fire yet (race on some platforms),
+		// force the state transition based on the promise resolution.
+		if (state !== "ready") {
+			updateDownloaded = true;
+			downloadProgress = 100;
+			setState("ready");
+		}
 	} catch (err) {
+		console.warn("[updater] downloadUpdate() rejected:", err);
 		lastError = (err as Error)?.message ?? String(err);
 		setState("error");
 	}

src/mainview/pages/Settings.tsx

@@ -129,7 +129,13 @@ export default function SettingsPage() {
   async function handleUpdateDownload() {
     setUpdateBusy('downloading')
     try {
-      await invoke('app_update_download')
+      // Returns a status snapshot; if the final state is 'error', the
+      // autoUpdater rejected (network, signature, etc.) and we should surface
+      // that to the user instead of just re-enabling the button.
+      const snapshot = await invoke('app_update_download')
+      if (snapshot?.state === 'error' && snapshot.error) {
+        toast(snapshot.error, 'destructive')
+      }
     } catch (e) {
       toast(
         t('settings.updateStateError') +