Introduce a lint-docs script and Makefile target for common
documentation naming and placement checks. Expand docs/README.md
with layout and translation conventions, and update CONTRIBUTING.md
to point contributors to the new docs guidance and validation step.
- CONTRIBUTING.md: change link from zh-hans to en locale
- CONTRIBUTING.zh.md: fix NBSP causing surrounding text to be absorbed into the link
- Both files now use proper markdown link syntax
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