fix(auth): add retry and logging for token refresh failures

Add a single retry with a 1-second delay in the 401 interceptor's
doRefresh() before giving up on token renewal. This handles transient
failures like brief network blips or server restarts without immediately
logging the user out.

Also log refresh failures via console.warn so the reason is visible
in browser DevTools for easier diagnosis.

Ref: #2391

frontend/src/helpers/fetcher.ts

@@ -38,11 +38,20 @@ async function doRefresh(): Promise<string | null> {
 	try {
 		await refreshToken(true)
 		return getToken()
-	} catch {
-		// Refresh failed. Don't remove the token here — in a multi-tab scenario,
-		// another tab may have successfully rotated the refresh token, and clearing
-		// localStorage would log out that tab too. Let the caller decide.
-		return null
+	} catch (_e) {
+		// Single retry after a short delay for transient failures (network
+		// blip, server restart). If this also fails, give up.
+		try {
+			await new Promise(resolve => setTimeout(resolve, 1000))
+			await refreshToken(true)
+			return getToken()
+		} catch (retryErr) {
+			// Refresh failed. Don't remove the token here — in a multi-tab scenario,
+			// another tab may have successfully rotated the refresh token, and clearing
+			// localStorage would log out that tab too. Let the caller decide.
+			console.warn('[Vikunja] Token refresh failed:', retryErr)
+			return null
+		}
 	}
 }