fix: release v0.2.1 lesson deletes and large uploads

- Raise Traefik read timeout to 1h (compose dev/prod + k3s HelmChartConfig)
  so admin video uploads up to 200MB no longer 502 mid-upload.
- Migration 0029: cascade watch/quiz history on lesson delete and unlink
  dependent lessons, so removing a lesson or chapter stops 500ing.
- Add the Apollo cluster Helm overlay (values-apollo.yaml) for the deployed
  environment.
- k3s Traefik chart config also enables access logs, cross-namespace
  IngressRoutes, and fixes the Prometheus scrape port.

Bump appVersion/product.go/values tags to 0.2.1; chart version 0.2.3.

backend/internal/api/product.go

@@ -583,7 +583,7 @@ func (s *Server) handleMeta(w http.ResponseWriter, r *http.Request) {
 }
 
 func appBuild() (version, built string) {
-	version = "0.2.0"
+	version = "0.2.1"
 	built = "dev"
 	info, ok := debug.ReadBuildInfo()
 	if !ok {
@@ -594,7 +594,7 @@ func appBuild() (version, built string) {
 			built = setting.Value[:10]
 		}
 		if setting.Key == "vcs.revision" && len(setting.Value) >= 7 {
-			version = "0.2.0+" + setting.Value[:7]
+			version = "0.2.1+" + setting.Value[:7]
 		}
 	}
 	return version, built