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/kill/kill.go

@@ -0,0 +1,43 @@
+package kill
+
+import (
+	"fmt"
+	"os/exec"
+
+	"github.com/forust/gosleep-timer/config"
+	"github.com/forust/gosleep-timer/modules"
+)
+
+type KillModule struct{}
+
+func (m *KillModule) Name() string {
+	return "kill"
+}
+
+func (m *KillModule) Enabled(cfg *config.Modules) bool {
+	return cfg.Kill != nil && cfg.Kill.Enabled && len(cfg.Kill.Processes) > 0
+}
+
+func (m *KillModule) BuildCmds(ctx *modules.ModuleContext, stage modules.Stage) []string {
+	if stage != modules.StagePre {
+		return nil
+	}
+
+	var cmds []string
+	for _, proc := range ctx.Config.Kill.Processes {
+		if proc == "" {
+			continue
+		}
+		cmds = append(cmds, fmt.Sprintf("pkill %s", proc))
+	}
+	return cmds
+}
+
+func (m *KillModule) Validate() error {
+	_, err := exec.LookPath("pkill")
+	return err
+}
+
+func init() {
+	modules.Register(&KillModule{})
+}