M1: start active-window sensor wired to the controller

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/antidriftd/main.go

@@ -3,11 +3,13 @@
 package main
 
 import (
+	"context"
 	"log"
 	"os/exec"
 	"runtime"
 	"time"
 
+	"antidrift/internal/evidence"
 	"antidrift/internal/session"
 	"antidrift/internal/store"
 	"antidrift/internal/web"
@@ -28,6 +30,9 @@ func main() {
 	srv := web.NewServer(ctrl)
 	srv.Init() // re-arm or expire a restored Active session
 
+	src := evidence.NewSource()
+	go src.Watch(context.Background(), ctrl.RecordWindow)
+
 	go openBrowser("http://" + addr)
 
 	log.Printf("antidriftd listening on http://%s", addr)