feat: stabilize API startup and lifecycle management

- Refactor server initialization to separate concerns and improve error handling.
- Implement centralized environment validation using Zod.
- Introduce database, Redis, and queue lifecycle management.
- Add health check endpoints for liveness and readiness.
- Enhance error handling middleware for better response structure.
- Implement rate limiting for API endpoints.
- Add request ID middleware for traceability.
- Create Sequelize CLI configuration and baseline migration for schema management.
- Establish CI workflow with Gitea for testing and syntax checks.
- Document foundational changes and migration strategy in PHASE_0_FOUNDATION_STABILIZATION.md.
- Add Docker Compose configuration for local development and testing.
- Implement unit and integration tests for critical functionality.

tests/unit/env.config.test.js

@@ -0,0 +1,21 @@
+const { validateEnvironment, getOptionalFeatureStatus } = require("../../app/config/env.config");
+
+const valid = {
+  NODE_ENV: "test", PORT: "3070", DB_HOST: "localhost", DB_PORT: "3306", DB_NAME: "test",
+  DB_USER: "test", DB_PASSWORD: "", JWT_SECRET: "a".repeat(32), REFRESH_TOKEN_SECRET: "b".repeat(32),
+  REDIS_HOST: "localhost", REDIS_PORT: "6379", FRONTEND_URL: "http://localhost:3000",
+};
+
+describe("environment validation", () => {
+  test("accepts the critical API configuration", () => {
+    expect(validateEnvironment(valid)).toMatchObject({ PORT: 3070, DB_NAME: "test", RUN_CRON: false });
+  });
+
+  test("fails safely and names invalid variables without values", () => {
+    expect(() => validateEnvironment({ ...valid, JWT_SECRET: "short" })).toThrow("JWT_SECRET");
+  });
+
+  test("keeps mail and S3 optional", () => {
+    expect(getOptionalFeatureStatus(valid)).toMatchObject({ mail: false, s3: false });
+  });
+});