feat: .NET appsettings files in repos

appsettings.json and appsettings.<Environment>.json tracked by git are
listed under Repos, keys named as .NET names them (ConnectionStrings:Default).

- The secret patterns pick the keys, the rest hidden, with
  dotnet.secretPatterns for .NET files' own.
- An App Service Key Vault reference, @Microsoft.KeyVault(…), is marked
  as a reference; a BOM at the start is fine.
- A .NET icon, themeable with dotnetColor.

internal/ui/styles/styles.go

@@ -36,6 +36,7 @@ type Styles struct {
 	KindRepo       lipgloss.Style
 	Spring         lipgloss.Style // Spring Boot config files
 	Compose        lipgloss.Style // Docker Compose files
+	Dotnet         lipgloss.Style // .NET appsettings files
 
 	// themed marks the selection colours as set by the theme, so
 	// OnBackground leaves them.
@@ -74,6 +75,7 @@ func Default() Styles {
 		KindRepo:       lipgloss.NewStyle().Foreground(lipgloss.Magenta),
 		Spring:         lipgloss.NewStyle().Foreground(lipgloss.Green),
 		Compose:        lipgloss.NewStyle().Foreground(lipgloss.Blue),
+		Dotnet:         lipgloss.NewStyle().Foreground(lipgloss.BrightMagenta),
 	}
 }