Make test deployment version observable

The test server health endpoint now reports 0.2.1 so deployments that include start-end frame routing can be verified directly after restart.

Constraint: Deployment verification relies on /health because the service does not expose a build SHA endpoint.

Confidence: high

Scope-risk: narrow

Directive: Keep this value in sync with test deployments until a real build metadata endpoint exists.

Tested: go test ./...

Tested: make build

Tested: GOOS=linux GOARCH=amd64 go build -o dist/popiartserver-linux-amd64 ./cmd/popiartserver

internal/server/server.go

@@ -82,7 +82,7 @@ func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]any{
 		"ok":      true,
 		"service": "popiart-server-dev",
-		"version": "0.2.0",
+		"version": "0.2.1",
 		"time":    time.Now().UTC().Format(time.RFC3339),
 	})
 }