Stage 0: scaffold monorepo, backend skeleton, docs, CI

- go.work (Go 1.26.3) with backend module; deps added incrementally (gin+zap only)

- backend: /healthz + /readyz, env config, graceful shutdown

- docs: ARCHITECTURE, FUNCTIONAL (+ru mirror), TESTING

- PLAN.md (stage tracker + per-stage open details) and CLAUDE.md (per-stage workflow)

- .gitea go-unit CI (gofmt/vet/build/test)

backend/internal/server/server_test.go

@@ -0,0 +1,22 @@
+package server
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"go.uber.org/zap/zaptest"
+)
+
+// TestProbes verifies that the infrastructure probes answer 200 OK.
+func TestProbes(t *testing.T) {
+	srv := New(":0", zaptest.NewLogger(t))
+	for _, path := range []string{"/healthz", "/readyz"} {
+		req := httptest.NewRequest(http.MethodGet, path, nil)
+		rec := httptest.NewRecorder()
+		srv.http.Handler.ServeHTTP(rec, req)
+		if rec.Code != http.StatusOK {
+			t.Fatalf("%s: status = %d, want %d", path, rec.Code, http.StatusOK)
+		}
+	}
+}