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/SECURITY.md

@@ -0,0 +1,28 @@
+# Security Policy
+
+## Reporting a vulnerability
+
+Please **do not** open a public issue for security vulnerabilities.
+
+Report privately instead:
+
+- Open a [private security advisory](https://github.com/OWNER/REPO/security/advisories/new), or
+- Email the maintainers (see repository profile for contact).
+
+You should receive a response within 7 days. Please include:
+
+- Affected version(s) / commit
+- Steps to reproduce
+- Impact description
+
+## Supported versions
+
+| Version | Supported |
+|---------|-----------|
+| latest  | ✅ |
+| older   | ❌ (best effort) |
+
+## Disclosure
+
+We appreciate responsible disclosure. Once a fix is released, we will
+acknowledge the reporter in the release notes (unless anonymity is requested).