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

history/stats.go

@@ -0,0 +1,54 @@
+package history
+
+import "time"
+
+type Stats struct {
+	TotalRuns       int
+	CompletedRuns   int
+	KilledRuns      int
+	ErrorRuns       int
+	TotalDuration   time.Duration
+	AvgDuration     time.Duration
+	MostUsedProfile string
+	LastRun         *Record
+}
+
+func Calculate(records []Record) Stats {
+	var s Stats
+	profileCount := make(map[string]int)
+	s.TotalRuns = len(records)
+
+	for _, r := range records {
+		switch r.Status {
+		case "completed":
+			s.CompletedRuns++
+		case "killed":
+			s.KilledRuns++
+		case "error":
+			s.ErrorRuns++
+		}
+
+		profileCount[r.Profile]++
+
+		d, err := time.ParseDuration(r.Duration)
+		if err == nil {
+			s.TotalDuration += d
+		}
+
+		s.LastRun = &r
+	}
+
+	if s.TotalRuns > 0 {
+		s.AvgDuration = time.Duration(int64(s.TotalDuration) / int64(s.TotalRuns))
+	}
+
+	maxCount := 0
+	for name, count := range profileCount {
+		if count > maxCount {
+			maxCount = count
+			s.MostUsedProfile = name
+		}
+	}
+
+	return s
+}