feat: initial gosleep-timer implementation

Go TUI sleep timer with modular architecture.
- Config: YAML-based, profile inheritance, auto WM detection
- Engine: timer, executor, stage pipeline (pre→timer→post)
- Modules: workspace (niri/hyprland/kde), media, lock, kill,
  notify, sound, brightness, mute, custom, script
- TUI: bubbletea app with profiles, module toggles, progress bar
- CLI: run, list-profiles, export, import, history, stats
- History: JSONL log with statistics
- QR: config export as ASCII QR

tui/qr.go

@@ -0,0 +1,17 @@
+package tui
+
+import (
+    "fmt"
+    qrcode "github.com/skip2/go-qrcode"
+)
+
+// GenerateQR returns a string of the QR code for the given data
+func GenerateQR(data string) (string, error) {
+    qr, err := qrcode.New(data, qrcode.Medium)
+    if err != nil {
+        return "", fmt.Errorf("qr generate: %w", err)
+    }
+    // Convert to ASCII art
+    art := qr.ToString(true)
+    return art, nil
+}