feat: complete Taro dual-platform migration

[Young581]

Summary

• Preserve web/ as the Golden Reference and make miniProgram/ the only Taro client.
• Add the React 18 + Taro 4.2.1 H5/WeApp demo flows, domain repository, and platform adapters.
• Add responsive legacy H5 routes, branded navigation, deterministic media fixtures, doctor scripts, and the WeChat E2E harness.
• Consolidate the cloud skeleton with the local implementation and remove duplicate and temporary mini-app projects.

Validation

• npm run lint
• npx tsc --noEmit
• npm test (6/6)
• npm run build:h5
• npm run build:weapp
• H5 visual review at 360, 390, 430, 820, and 1280 px.

Notes

• WeChat DevTools automation and real-device smoke testing remain pending until the local DevTools service port is enabled.
• H5 currently emits the documented 356 KiB entry-size warning.