chore: add community standards (CoC, contributing, security, templates)

Adds the seven files needed to pass the GitHub Community Standards checklist:

- CODE_OF_CONDUCT.md (Contributor Covenant 2.1)
- CONTRIBUTING.md (scope, dev setup, tests, PR rules; points users at
  feder-cr/firefox-stealth for C++/spoofing issues)
- SECURITY.md (private vuln reporting via GH advisories or email,
  out-of-scope items redirected to firefox-stealth / Mozilla)
- .github/ISSUE_TEMPLATE/bug_report.yml
- .github/ISSUE_TEMPLATE/feature_request.yml
- .github/ISSUE_TEMPLATE/config.yml (disables blank issues, links to
  security advisories, firefox-stealth, and discussions)
- .github/PULL_REQUEST_TEMPLATE.md

CODE_OF_CONDUCT.md

@@ -0,0 +1,33 @@
+# Code of Conduct
+
+This project follows the [Contributor Covenant, v2.1](https://www.contributor-covenant.org/version/2/1/code_of_conduct/).
+
+## Our Pledge
+
+We pledge to make participation in our community a harassment-free experience for everyone.
+
+## Standards
+
+Examples of behavior that contributes to a positive environment:
+
+- Using welcoming and inclusive language
+- Being respectful of differing viewpoints and experiences
+- Gracefully accepting constructive criticism
+- Focusing on what is best for the community
+
+Examples of unacceptable behavior:
+
+- The use of sexualized language or imagery
+- Trolling, insulting or derogatory comments, and personal or political attacks
+- Public or private harassment
+- Publishing others' private information without explicit permission
+
+## Enforcement
+
+Instances of unacceptable behavior may be reported by contacting the maintainer at **federico.elia.majo@gmail.com**. All complaints will be reviewed and investigated and will result in a response that is deemed necessary and appropriate to the circumstances.
+
+The maintainer is obligated to maintain confidentiality with regard to the reporter of an incident.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant](https://www.contributor-covenant.org), version 2.1, available at https://www.contributor-covenant.org/version/2/1/code_of_conduct.html.