[Feat] Replace the Default App Icon

[pranavkonidena]

Is your feature request related to a problem? Please describe.
The current app uses Flutter's default app icon, which lacks branding and makes the app feel generic. This can diminish the app's professionalism and make it less recognizable to users.

Describe the solution you'd like
Replace the default app icon with a custom Taskly icon that reflects the app's purpose and brand identity.
The icon should feature a minimalistic design, incorporating elements like a clipboard, checkmark, or a stylized "T".
Ensure the icon is exported in all required resolutions to support different devices and platforms (iOS and Android).

Additional context
Assets: Provide the icon in multiple resolutions (e.g., 48x48, 72x72, 96x96, 192x192 for Android; 180x180, 120x120 for iOS).