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_test.go

@@ -0,0 +1,162 @@
+package summary
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestPushClient_Push(t *testing.T) {
+	var received MetricsPayload
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		if ct := r.Header.Get("Content-Type"); ct != "application/json" {
+			t.Errorf("expected Content-Type application/json, got %s", ct)
+		}
+		if err := json.NewDecoder(r.Body).Decode(&received); err != nil {
+			t.Errorf("failed to decode body: %v", err)
+		}
+		w.WriteHeader(http.StatusCreated)
+	}))
+	defer server.Close()
+
+	client := NewPushClient(server.URL)
+	client.ctx = ExecutionContext{
+		Organization: "test-org",
+		Repository:   "test-repo",
+		Workflow:     "ci.yml",
+		Job:          "build",
+		RunID:        "12345",
+	}
+
+	summary := &RunSummary{
+		StartTime:       time.Now().Add(-time.Minute),
+		EndTime:         time.Now(),
+		DurationSeconds: 60.0,
+		SampleCount:     10,
+		CPUTotal:        StatSummary{Peak: 80.0, Avg: 50.0, P95: 75.0},
+	}
+
+	err := client.Push(context.Background(), summary)
+	if err != nil {
+		t.Fatalf("Push() error = %v", err)
+	}
+
+	if received.Execution.Organization != "test-org" {
+		t.Errorf("Organization = %q, want %q", received.Execution.Organization, "test-org")
+	}
+	if received.Execution.RunID != "12345" {
+		t.Errorf("RunID = %q, want %q", received.Execution.RunID, "12345")
+	}
+	if received.Summary.SampleCount != 10 {
+		t.Errorf("SampleCount = %d, want %d", received.Summary.SampleCount, 10)
+	}
+}
+
+func TestPushClient_Push_NilSummary(t *testing.T) {
+	client := NewPushClient("http://localhost:9999")
+	err := client.Push(context.Background(), nil)
+	if err != nil {
+		t.Errorf("Push(nil) error = %v, want nil", err)
+	}
+}
+
+func TestPushClient_Push_ServerError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	client := NewPushClient(server.URL)
+	client.ctx = ExecutionContext{RunID: "test"}
+
+	err := client.Push(context.Background(), &RunSummary{})
+	if err == nil {
+		t.Error("Push() expected error for 500 response, got nil")
+	}
+}
+
+func TestPushClient_Push_ConnectionError(t *testing.T) {
+	client := NewPushClient("http://localhost:1") // Invalid port
+	client.ctx = ExecutionContext{RunID: "test"}
+
+	err := client.Push(context.Background(), &RunSummary{})
+	if err == nil {
+		t.Error("Push() expected error for connection failure, got nil")
+	}
+}
+
+func TestExecutionContextFromEnv(t *testing.T) {
+	// Save and restore env
+	origVars := map[string]string{
+		"GITHUB_REPOSITORY_OWNER": "",
+		"GITHUB_REPOSITORY":       "",
+		"GITHUB_WORKFLOW":         "",
+		"GITHUB_JOB":              "",
+		"GITHUB_RUN_ID":           "",
+	}
+	for k := range origVars {
+		origVars[k] = getEnvWithFallback(k)
+	}
+	defer func() {
+		for k, v := range origVars {
+			if v == "" {
+				t.Setenv(k, "")
+			}
+		}
+	}()
+
+	t.Setenv("GITHUB_REPOSITORY_OWNER", "my-org")
+	t.Setenv("GITHUB_REPOSITORY", "my-org/my-repo")
+	t.Setenv("GITHUB_WORKFLOW", "CI")
+	t.Setenv("GITHUB_JOB", "test")
+	t.Setenv("GITHUB_RUN_ID", "999")
+
+	ctx := ExecutionContextFromEnv()
+
+	if ctx.Organization != "my-org" {
+		t.Errorf("Organization = %q, want %q", ctx.Organization, "my-org")
+	}
+	if ctx.Repository != "my-org/my-repo" {
+		t.Errorf("Repository = %q, want %q", ctx.Repository, "my-org/my-repo")
+	}
+	if ctx.Workflow != "CI" {
+		t.Errorf("Workflow = %q, want %q", ctx.Workflow, "CI")
+	}
+	if ctx.Job != "test" {
+		t.Errorf("Job = %q, want %q", ctx.Job, "test")
+	}
+	if ctx.RunID != "999" {
+		t.Errorf("RunID = %q, want %q", ctx.RunID, "999")
+	}
+}
+
+func TestExecutionContextFromEnv_GiteaFallback(t *testing.T) {
+	t.Setenv("GITHUB_RUN_ID", "")
+	t.Setenv("GITEA_RUN_ID", "gitea-123")
+
+	ctx := ExecutionContextFromEnv()
+
+	if ctx.RunID != "gitea-123" {
+		t.Errorf("RunID = %q, want %q (Gitea fallback)", ctx.RunID, "gitea-123")
+	}
+}
+
+func TestPushClient_ExecutionContext(t *testing.T) {
+	client := NewPushClient("http://example.com")
+	client.ctx = ExecutionContext{
+		Organization: "org",
+		Repository:   "repo",
+		RunID:        "run",
+	}
+
+	ctx := client.ExecutionContext()
+	if ctx.Organization != "org" {
+		t.Errorf("Organization = %q, want %q", ctx.Organization, "org")
+	}
+}