docs: add release guide and link from README

[oahsiao]

Adds a formal, version-controlled release guide and links it from the README.

What

• New docs/RELEASE.md documenting the verified release process:
  • Branch protection + 4 required checks
  • Versioning rules incl. the RELEASE shortcut (default = patch +1)
  • 8-step cut-a-release flow (branch -> PR -> merge -> tag merge commit)
  • Dual-arch (x64 + ARM64) build outputs
  • Gotchas (tag on merge commit, watch TUI, Node 20 deprecation)
• README EN + ZH build sections now link to the guide.

Docs only - no code or workflow changes.