chore: complete rename from go-upkeep to uptop

- Module path: gitea.lerkolabs.com/lerko/uptop
- Binary: cmd/uptop/
- All imports updated to full module path
- Env vars: UPKEEP_* → UPTOP_*
- Prometheus metrics: upkeep_* → uptop_*
- Default DB: uptop.db
- Docker image: lerko/uptop
- All docs, compose files, CI updated

Only remaining "go-upkeep" reference is the fork attribution in README.

internal/monitor/checker_test.go

@@ -2,7 +2,7 @@ package monitor
 
 import (
 	"crypto/tls"
-	"go-upkeep/internal/models"
+	"gitea.lerkolabs.com/lerko/uptop/internal/models"
 	"net"
 	"net/http"
 	"net/http/httptest"