Update MainWindow.vala

[itashia]

trafficstars

feat(weather): enhance details, add forecast & improve UI/UX

• Added humidity, dew point, and "feels like" temperature
• Introduced 5-day forecast popover with min/max temps & icons
• Improved layout: better spacing, margins, and icon size
• Added refresh button and responsive design tweaks
• Enhanced theming with precise weather-based styles
• Improved UX: clear loading state, conditional forecast button, better error handling
• Optimized performance by lazy-loading forecast data and efficient updates

[danirabbit]

Hey thanks for your contribution. But please separate each change into its own pull request. A single pull request should represent a single fix or feature. I won't review pull requests that group together several unrelated features