fix: detect stale PID files from recycled PIDs

The daemon startup check only used kill -0 to verify if the PID from
the PID file was alive. If the OS recycled that PID for an unrelated
process, hyprvoice would refuse to start with "daemon already running"
even though no hyprvoice instance was running.

Now also reads /proc/<pid>/cmdline to verify the process is actually
hyprvoice before treating it as a running daemon. If it's a different
process, the PID file is treated as stale and removed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/bus/bus.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"strconv"
+	"strings"
 	"syscall"
 )
 
@@ -99,6 +100,19 @@ func (pm *pidManager) isProcessAlive(pid int) bool {
 		return false
 	}
 
+	// Verify the process is actually hyprvoice and not a recycled PID
+	cmdline, err := os.ReadFile(fmt.Sprintf("/proc/%d/cmdline", pid))
+	if err != nil {
+		log.Printf("Process %d alive but cannot read cmdline, assuming stale: %v", pid, err)
+		return false
+	}
+
+	exe := string(cmdline)
+	if len(exe) == 0 || !strings.Contains(exe, "hyprvoice") {
+		log.Printf("Process %d is alive but is not hyprvoice (cmdline: %q), stale PID file", pid, exe)
+		return false
+	}
+
 	return true
 }