Add repo-standardizer skill: polish any GitHub repo surface (#2715)

* Add repo-standardizer skill: polish any GitHub repo surface

* fix(skill): remove non-string metadata and fix template README refs for vally lint

* docs(skill): drop markdown relative links from README language-switcher example

Vally valid-refs flagged ./README.md and ./README.zh.md as missing file
references; they are generated artifacts, not skill files. Keep the
example as plain text to satisfy the linter.

* fix(template): add missing language switcher to English README template

Align with README.zh.md template and SKILL.md switcher convention:
current language as plain text, other languages as relative links.

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Co-authored-by: programmingWTF <programmingWTF@users.noreply.github.com>

skills/repo-standardizer/templates/PR_TEMPLATE.md

@@ -0,0 +1,22 @@
+## Summary
+
+<!-- What does this PR do, in one or two sentences? -->
+
+## Related issues
+
+<!-- Link any related issues: Fixes #123 -->
+
+## Changes
+
+- [ ] Feature / fix implemented
+- [ ] Tests added or updated
+- [ ] Documentation updated (if needed)
+- [ ] Changelog entry added (if needed)
+
+## Testing
+
+<!-- How was this change tested? Include commands and expected output. -->
+
+## Screenshots (optional)
+
+<!-- If UI changes, add screenshots here. -->