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

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,40 @@
+<!--
+Thanks for your contribution! Please fill in the sections below.
+PRs that don't follow this template may be asked for revision before review.
+-->
+
+## Summary
+
+<!-- One or two sentences: what does this PR change and why? -->
+
+## Type of change
+
+<!-- Tick all that apply -->
+
+- [ ] Bug fix (non-breaking change that fixes an issue)
+- [ ] New feature (non-breaking change that adds functionality)
+- [ ] Breaking change (fix or feature that changes existing behavior)
+- [ ] Documentation only
+- [ ] Tests / CI / tooling
+
+## Related issues
+
+<!-- Link any related issues, e.g. "Closes #123", "Refs #456" -->
+
+## How was this tested?
+
+<!--
+Describe what you ran:
+- `pytest` (default, unit + integration)
+- `pytest -m e2e` (against the patched binary)
+- Manual repro steps, screenshots, etc.
+-->
+
+## Checklist
+
+- [ ] I have read [CONTRIBUTING.md](../CONTRIBUTING.md).
+- [ ] My commits follow [Conventional Commits](https://www.conventionalcommits.org/).
+- [ ] I added or updated tests covering the change.
+- [ ] `pytest` passes locally.
+- [ ] I updated `README.md` / `docs/` if user-visible behavior changed.
+- [ ] My change is in scope for this repo (Python wrapper / sampler / CLI / packaging — not the patched Firefox C++ source).