refactor: remove TUI, desktop web UI is now the default and only mode

- Remove internal/tui/ entirely (2600+ lines of Bubble Tea code)
- Remove bubbletea, bubbles, lipgloss direct dependencies
- `muyue` now launches desktop web UI (opens browser)
- CLI subcommands preserved (scan, install, setup, etc.)
- Unknown args passed as desktop flags (--port, --no-open)
- Update help text to reflect new default behavior

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

go.sum

@@ -14,8 +14,6 @@ github.com/charmbracelet/bubbletea v1.3.10 h1:otUDHWMMzQSB0Pkc87rm691KZ3SWa4KUlv
 github.com/charmbracelet/bubbletea v1.3.10/go.mod h1:ORQfo0fk8U+po9VaNvnV95UPWA1BitP1E0N6xJPlHr4=
 github.com/charmbracelet/colorprofile v0.4.1 h1:a1lO03qTrSIRaK8c3JRxJDZOvhvIeSco3ej+ngLk1kk=
 github.com/charmbracelet/colorprofile v0.4.1/go.mod h1:U1d9Dljmdf9DLegaJ0nGZNJvoXAhayhmidOdcBwAvKk=
-github.com/charmbracelet/harmonica v0.2.0 h1:8NxJWRWg/bzKqqEaaeFNipOu77YR5t8aSwG4pgaUBiQ=
-github.com/charmbracelet/harmonica v0.2.0/go.mod h1:KSri/1RMQOZLbw7AHqgcBycp8pgJnQMYYT8QZRqZ1Ao=
 github.com/charmbracelet/huh v1.0.0 h1:wOnedH8G4qzJbmhftTqrpppyqHakl/zbbNdXIWJyIxw=
 github.com/charmbracelet/huh v1.0.0/go.mod h1:5YVc+SlZ1IhQALxRPpkGwwEKftN/+OlJlnJYlDRFqN4=
 github.com/charmbracelet/lipgloss v1.1.0 h1:vYXsiLHVkK7fp74RkV7b2kq9+zDLoEU4MZoFqR/noCY=