Add TUI for managing sandbox profile, relicense to GPLv3

- Add Go/Bubble Tea TUI app under tui/ with dashboard (status checks,
  launch, validate) and profile editor (commands, filesystem, network,
  environment sub-tabs)
- Add Makefile targets: tui, tui-build, tui-install
- Add CI step to build TUI
- Relicense MIT -> GPL-3.0
- Rewrite wrapper to resolve real opencode binary from PATH (supports
  brew, npm, volta)
- Add PATH ordering detection to install script
- Expand README with how-it-works diagram, TUI docs, keybinding table

tui/styles.go

@@ -0,0 +1,77 @@
+package main
+
+import "github.com/charmbracelet/lipgloss"
+
+var (
+	green  = lipgloss.Color("#04B575")
+	red    = lipgloss.Color("#FF4646")
+	yellow = lipgloss.Color("#FFA500")
+	blue   = lipgloss.Color("#7D56F4")
+	gray   = lipgloss.Color("#666666")
+
+	titleStyle = lipgloss.NewStyle().
+			Bold(true).
+			Foreground(lipgloss.Color("#FAFAFA")).
+			Background(blue).
+			Padding(0, 2)
+
+	tabStyle = lipgloss.NewStyle().
+			Foreground(gray).
+			Padding(0, 2)
+
+	activeTabStyle = lipgloss.NewStyle().
+			Bold(true).
+			Foreground(lipgloss.Color("#FAFAFA")).
+			Background(blue).
+			Padding(0, 2)
+
+	checkOKStyle = lipgloss.NewStyle().
+			Foreground(green).
+			Bold(true)
+
+	checkFailStyle = lipgloss.NewStyle().
+			Foreground(red).
+			Bold(true)
+
+	labelStyle = lipgloss.NewStyle().
+			Width(26).
+			Foreground(lipgloss.Color("#AAAAAA"))
+
+	detailStyle = lipgloss.NewStyle().
+			Foreground(gray)
+
+	boxStyle = lipgloss.NewStyle().
+			Border(lipgloss.RoundedBorder()).
+			BorderForeground(gray).
+			Padding(0, 1)
+
+	activeBoxStyle = lipgloss.NewStyle().
+			Border(lipgloss.RoundedBorder()).
+			BorderForeground(blue).
+			Padding(0, 1)
+
+	cursorStyle = lipgloss.NewStyle().
+			Foreground(yellow).
+			Bold(true)
+
+	dirtyStyle = lipgloss.NewStyle().
+			Foreground(yellow).
+			Bold(true)
+
+	helpStyle = lipgloss.NewStyle().
+			Foreground(gray).
+			Italic(true)
+
+	statusBarStyle = lipgloss.NewStyle().
+			Background(lipgloss.Color("#333333")).
+			Foreground(lipgloss.Color("#FFFFFF")).
+			Padding(0, 1)
+
+	errorStyle = lipgloss.NewStyle().
+			Foreground(red).
+			Bold(true)
+
+	successStyle = lipgloss.NewStyle().
+			Foreground(green).
+			Bold(true)
+)