chore: adopt Biome + Stylelint, modernize CI/CD, add security/support docs, minor JS fixes

- Linting/format
  - Replace ESLint/Prettier with Biome; remove old configs; add `biome.json`; update scripts
  - Tailwind-friendly `.stylelintrc.yaml`; Stylelint and Biome pass
  - Enable Biome across `modules/**`; prune legacy JS globals; ignore oversized `devicon.json`

- Code fixes
  - `hb-theme.js`: avoid assignment-in-expressions; clearer dataset updates
  - `hugoblox-slides.js`: fix inner var scope (var → let); apply formatting

- CI/CD
  - Split lint/build workflows; add path filters; Node via Corepack (pnpm from package.json)
  - Hugo pinned to env `HUGO_VERSION`; add consistency check vs `starters/academic-cv/hugoblox.yaml`
  - Nightly starters matrix build (academic-cv, landing-page); CodeQL weekly; resource caches

- Workflows/Community
  - Greeter: switch to `pull_request_target`; add Contributor Guide to PR message
  - PR labeler for path-based labels

- Repo policies/docs
  - `CODEOWNERS` for `@gcushen`
  - `SECURITY.md`, `SUPPORT.md`
  - Documented branch protection in `.github/settings.yml`
  - Move `CODE_OF_CONDUCT.md` to `.github/`

- docs(zh): update `README.zh.md` translation

Notes:
- pnpm is sourced from `package.json: packageManager` via Corepack; no hard-coded pnpm versions in CI.

CONTRIBUTING.md

@@ -291,4 +291,4 @@ Every contribution matters — whether it's fixing a typo, adding a translation,
 
 _Questions? Join our [Discord](https://discord.gg/z8wNYzb) or start a [Discussion](https://github.com/HugoBlox/hugo-blox-builder/discussions)._
 
-_This project follows the [Contributor Covenant Code of Conduct](CODE_OF_CONDUCT.md)._
+_This project follows the [Contributor Covenant Code of Conduct](.github/CODE_OF_CONDUCT.md)._