Add ShowNotification API: inline notification bar in main window

[Copilot]

ShowMsg relies on OS toast notifications, which can be silently blocked, dismissed, or missed entirely — making it unreliable for plugins that need guaranteed user-visible feedback.

Changes

• NotificationSeverity enum (Flow.Launcher.Plugin) — Informational, Success, Warning, Error
• IPublicAPI.ShowNotification — new method signature:

  void ShowNotification(string title, string subTitle = "", NotificationSeverity severity = NotificationSeverity.Informational);

• MainViewModel — adds InlineNotificationIsOpen/Title/Message/Severity properties (Fody-notified) and ShowInlineNotification() with dispatcher guard
• MainWindow.xaml — inserts a ui:InfoBar between the query box and results list, two-way bound to the ViewModel; collapses when IsOpen=false so it takes no space at rest
• Notification.ShowInline — maps NotificationSeverity → InfoBarSeverity, resolves MainViewModel from IoC, calls ShowInlineNotification
• PublicAPIInstance + JsonRPCPublicAPI — wire ShowNotification through to Notification.ShowInline, making the API available to both C# and JsonRPC (Python/Node.js) plugins

Result

Plugins call ShowNotification and a styled, dismissable bar appears inside the Flow Launcher window — unaffected by OS notification settings, guaranteed visible whenever the window is open.

context.API.ShowNotification("Done", "Results copied to clipboard", NotificationSeverity.Success);
context.API.ShowNotification("Warning", "Rate limit approaching", NotificationSeverity.Warning);

[HorridModz]

This sounds awesome! I can't see what it looks like, of course, but I'll have to try it out when I get a chance. I think the Notification Severity is a nice touch.

[VictoriousRaptor]

This sounds awesome! I can't see what it looks like, of course, but I'll have to try it out when I get a chance. I think the Notification Severity is a nice touch.

I'm sorry but this PR is just a click to copilot and see if it can solve that issue, not something we're bringing into the project yet.

[HorridModz]

This sounds awesome! I can't see what it looks like, of course, but I'll have to try it out when I get a chance. I think the Notification Severity is a nice touch.

I'm sorry but this PR is just a click to copilot and see if it can solve that issue, not something we're bringing into the project yet.

Yes, of course. But I do hope this makes it into Flow.Launcher (in whatever form that may be); the idea sounds fantastic.