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

modules/script/script.go

@@ -0,0 +1,40 @@
+package script
+
+import (
+	"fmt"
+
+	"github.com/forust/gosleep-timer/config"
+	"github.com/forust/gosleep-timer/modules"
+)
+
+type ScriptModule struct{}
+
+func (m *ScriptModule) Name() string {
+	return "script"
+}
+
+func (m *ScriptModule) Enabled(cfg *config.Modules) bool {
+	return cfg.Script != nil && cfg.Script.Enabled && cfg.Script.Path != ""
+}
+
+func (m *ScriptModule) BuildCmds(ctx *modules.ModuleContext, stage modules.Stage) []string {
+	scriptPath := ctx.Config.Script.Path
+	switch stage {
+	case modules.StagePre:
+		return []string{fmt.Sprintf("%s pre %s %s", scriptPath, ctx.Profile, ctx.Duration)}
+	case modules.StagePost:
+		return []string{fmt.Sprintf("%s post %s %s", scriptPath, ctx.Profile, ctx.Duration)}
+	}
+	return nil
+}
+
+func (m *ScriptModule) Validate() error {
+	// Validation happens after config is loaded, so we check at registration time
+	// that the module itself is valid, but path is per-profile.
+	// Return nil here; path validation happens at runtime in BuildCmds.
+	return nil
+}
+
+func init() {
+	modules.Register(&ScriptModule{})
+}