feat: add Timeweb Cloud provider for Woodpecker CI autoscaler

- Implement timewebcloud provider with DeployAgent, RemoveAgent, ListDeployedAgentNames
- Add minimal HTTP API client for Timeweb Cloud (create/list/delete servers)
- Register provider in main.go with CLI flags
- Add timeweb-list and timeweb-tester utilities
- Include Dockerfile and docker-compose.yml for deployment
- Update DEPLOY.md with verified OS/preset IDs

engine/const.go

@@ -0,0 +1,9 @@
+package engine
+
+import "fmt"
+
+var (
+	LabelPrefix = "wp.autoscaler/"
+	LabelPool   = fmt.Sprintf("%spool", LabelPrefix)
+	LabelImage  = fmt.Sprintf("%simage", LabelPrefix)
+)