feat: add Go/Bubble Tea TUI rewrite (apps/tui-go)

Reimplement the TUI in Go using Bubble Tea, replacing the Kotlin/Tamboui
app. Same WebSocket protocol, soft-rounded layout with blue accent theme.

apps/tui-go/cmd/preview/main.go

@@ -0,0 +1,30 @@
+// Command preview prints a single static TUI frame for screenshotting.
+// Usage: preview <kind> [cols] [rows]
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+
+	"github.com/charmbracelet/lipgloss"
+	"github.com/correx/tui-go/internal/app"
+	"github.com/muesli/termenv"
+)
+
+func main() {
+	lipgloss.SetColorProfile(termenv.TrueColor)
+
+	kind := "idle"
+	if len(os.Args) > 1 {
+		kind = os.Args[1]
+	}
+	cols, rows := 140, 36
+	if len(os.Args) > 2 {
+		cols, _ = strconv.Atoi(os.Args[2])
+	}
+	if len(os.Args) > 3 {
+		rows, _ = strconv.Atoi(os.Args[3])
+	}
+	fmt.Print(app.PreviewFrame(kind, cols, rows))
+}