fix: rsync double SSH spec in RunRemote, restore dropped flags in Run

- Fix Bug A: RunRemote was re-prefixing destination with user@host: when
  engine.go:135 already pre-prefixed it for remote-to-remote, causing
  "admin@host:admin@host:/path" to be passed to rsync
- Fix Bug B: Run used args[1:] when inserting -e ssh, silently dropping
  the first rsync flag (e.g. -aP became flag-less)
- Fix Bug C: RunRemote extracted source/dest in wrong order for pull
  direction (buildArgs reverses them but RunRemote assumed push order)
- Add rsync_runner_test.go covering buildArgs, RunRemote prefixing,
  and flag preservation

cmd/server/main.go

@@ -20,7 +20,7 @@ import (
 	"github.com/syncserver/internal/syncengine"
 )
 
-var version = "1.0.36"
+var version = "1.0.37"
 
 func main() {
 	cfgPath := flag.String("config", "", "Path to config.yaml")