feat: release configurable API response contracts

Define reusable response bodies in .api with typed code mappings, per-route overrides and matching OpenAPI schemas. Add application and callback encoders, early response policy selection, and isolated remote-consumer release verification.

Release v0.8.0-preview after full race, vet, build and local MySQL workflow acceptance.

openapi/codeTypes_test.go

@@ -0,0 +1,42 @@
+package openapi_test
+
+import (
+	"testing"
+
+	"git.yuntuo.hk/k2safe/go-omni/openapi"
+	"git.yuntuo.hk/k2safe/go-omni/response"
+)
+
+func TestResponseCodeSchemaUsesGoWidths(t *testing.T) {
+	for _, kind := range []string{"string", "int32", "int64", "integer"} {
+		cfg := response.Config{CodeType: kind}
+		wantType, wantFormat := "string", ""
+		if kind != "string" {
+			cfg.SuccessCode = 200
+			cfg.ErrorCode = 9999
+			wantType = "integer"
+		}
+		if kind == "int32" || kind == "int64" {
+			wantFormat = kind
+		}
+		for _, nested := range []bool{false, true} {
+			if nested {
+				cfg.Body = map[string]any{"result": map[string]any{"code": "${code}"}}
+				cfg.ErrorBody = cfg.Body
+			}
+			for _, data := range []*openapi.Schema{nil, {Type: "object"}} {
+				schema, err := openapi.EnvelopeWith(data, cfg)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if nested {
+					schema = schema.Properties["result"]
+				}
+				code := schema.Properties["code"]
+				if code.Type != wantType || code.Format != wantFormat {
+					t.Fatalf("%s: %+v", kind, code)
+				}
+			}
+		}
+	}
+}