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>

internal/summary/push.go

@@ -0,0 +1,106 @@
+// ABOUTME: HTTP client for pushing run summaries to the metrics receiver.
+// ABOUTME: Reads execution context from GitHub Actions style environment variables.
+package summary
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"time"
+)
+
+// ExecutionContext holds GitHub Actions style identifiers for a workflow run
+type ExecutionContext struct {
+	Organization string `json:"organization"`
+	Repository   string `json:"repository"`
+	Workflow     string `json:"workflow"`
+	Job          string `json:"job"`
+	RunID        string `json:"run_id"`
+}
+
+// MetricsPayload is the complete payload sent to the receiver
+type MetricsPayload struct {
+	Execution ExecutionContext `json:"execution"`
+	Summary   RunSummary       `json:"run_summary"`
+}
+
+// PushClient sends metrics to the receiver service
+type PushClient struct {
+	endpoint string
+	client   *http.Client
+	ctx      ExecutionContext
+}
+
+// NewPushClient creates a new push client configured from environment variables
+func NewPushClient(endpoint string) *PushClient {
+	return &PushClient{
+		endpoint: endpoint,
+		client: &http.Client{
+			Timeout: 30 * time.Second,
+		},
+		ctx: ExecutionContextFromEnv(),
+	}
+}
+
+// ExecutionContextFromEnv reads execution context from GitHub Actions environment variables
+func ExecutionContextFromEnv() ExecutionContext {
+	return ExecutionContext{
+		Organization: getEnvWithFallback("GITHUB_REPOSITORY_OWNER", "GITEA_REPO_OWNER"),
+		Repository:   getEnvWithFallback("GITHUB_REPOSITORY", "GITEA_REPO"),
+		Workflow:     getEnvWithFallback("GITHUB_WORKFLOW", "GITEA_WORKFLOW"),
+		Job:          getEnvWithFallback("GITHUB_JOB", "GITEA_JOB"),
+		RunID:        getEnvWithFallback("GITHUB_RUN_ID", "GITEA_RUN_ID"),
+	}
+}
+
+func getEnvWithFallback(keys ...string) string {
+	for _, key := range keys {
+		if val := os.Getenv(key); val != "" {
+			return val
+		}
+	}
+	return ""
+}
+
+// Push sends the run summary to the receiver
+func (p *PushClient) Push(ctx context.Context, summary *RunSummary) error {
+	if summary == nil {
+		return nil
+	}
+
+	payload := MetricsPayload{
+		Execution: p.ctx,
+		Summary:   *summary,
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshaling payload: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, p.endpoint, bytes.NewReader(body))
+	if err != nil {
+		return fmt.Errorf("creating request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := p.client.Do(req)
+	if err != nil {
+		return fmt.Errorf("sending request: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	return nil
+}
+
+// ExecutionContext returns the current execution context
+func (p *PushClient) ExecutionContext() ExecutionContext {
+	return p.ctx
+}