[matteius]

The frontend toolchain now uses Node 26.13.0 LTS and TypeScript 7.0.2 for typechecking. Align Node engine requirements, typings, CI, Docker build defaults, and developer documentation, and update Preact to 11.2.0 and Babel core to 8.1.0.

TypeScript 7 runs through the official @typescript/native alias, alongside the TypeScript 6 compatibility API required by ESLint. Root TypeScript stays on 5.9.3 to satisfy the OpenAPI generator's compiler API and peer dependency. Contract declaration tests exercise the root compiler and the frontend's native compiler. Normalize MQTT test socket data to buffers for the Node 26 typings.

Validation on Node 26.13.0:

• Clean npm ci installs for the root and frontend.
• Production frontend build, frontend lint, and frontend/root/contract typechecks passed.
• All 87 frontend suites passed (1,027 tests).
• Contract lint, generated-artifact drift checks, contract tooling tests, and all 9 schema fixture tests passed.
• MQTT binary-payload smoke test passed.
• Production frontend dependency audit reports zero vulnerabilities.
• NodeSource 26.13.0 packages verified available for amd64 and arm64.

Full Docker builds and browser E2E tests were not run. Existing Jest development dependency advisories remain (17 moderate, 1 low); this upgrade does not resolve them.