Release DevEnv Manager 1.6.1 stable

[weidonglang]

Summary

DevEnv Manager 1.6.1 Stable closeout release.

• Moves the detailed page guide registry/rendering out of main.ts into features/help, completing the remaining practical [1.5.2 Patch][P2] 前端 main.ts 拆分为 feature modules，降低白屏和回归风险 #82 modularization gap.
• Bumps app metadata to 1.6.1.
• Updates README and update-manifest.json for the v1.6.1 installer.
• Uses the user-tested v1.6 behavior as accepted and prepares to close all remaining QA/open issues after release.

Release Asset

Prepared local installer asset:

• DevEnv.Manager_1.6.1_x64-setup.exe
• SHA256: 4980E5C33E3AB0A070FE50F35AF8D20F7826B4757C30B232FB26FE26B10E8DCE

Validation

npm run build
cargo test --all-targets
cargo clippy --all-targets -- -D warnings
py -3 scripts/check_repo_hygiene.py
npm run tauri:build

All passed locally.