Add Last Seen column and color-coded status badges in Machines table

- New Last Seen column showing last_seen_at timestamp per machine
- Status badges: online=green (success), offline=red (error), waking/pending=amber
- Update Machine interface with last_seen_at and created_at fields

cmd/server/main.go

@@ -20,7 +20,7 @@ import (
 	"github.com/syncserver/internal/syncengine"
 )
 
-var version = "1.0.40"
+var version = "1.0.41"
 
 func main() {
 	cfgPath := flag.String("config", "", "Path to config.yaml")