feat(collector): add HTTP push for metrics to receiver

Add push client that sends run summary to a configurable HTTP endpoint
on shutdown. Execution context is read from GitHub Actions style
environment variables (with Gitea fallbacks).

New flag: -push-endpoint <url>

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/collector/main.go

@@ -30,6 +30,7 @@ func main() {
 	logLevel := flag.String("log-level", defaultLogLevel, "Log level: debug, info, warn, error")
 	logFormat := flag.String("log-format", defaultLogFormat, "Output format: json, text")
 	topN := flag.Int("top", defaultTopN, "Number of top processes to include")
+	pushEndpoint := flag.String("push-endpoint", "", "HTTP endpoint to push metrics to (e.g., http://localhost:8080/api/v1/metrics)")
 	flag.Parse()
 
 	// Setup structured logging for application logs
@@ -58,6 +59,21 @@ func main() {
 	summaryWriter := summary.NewSummaryWriter(os.Stdout, *logFormat)
 	c.SetSummaryWriter(summaryWriter)
 
+	// Setup push client if endpoint is configured
+	if *pushEndpoint != "" {
+		pushClient := summary.NewPushClient(*pushEndpoint)
+		c.SetPushClient(pushClient)
+		execCtx := pushClient.ExecutionContext()
+		appLogger.Info("push client configured",
+			slog.String("endpoint", *pushEndpoint),
+			slog.String("organization", execCtx.Organization),
+			slog.String("repository", execCtx.Repository),
+			slog.String("workflow", execCtx.Workflow),
+			slog.String("job", execCtx.Job),
+			slog.String("run_id", execCtx.RunID),
+		)
+	}
+
 	// Setup signal handling for graceful shutdown
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()