docs: add community governance and contribution guidelines

- Add CONTRIBUTING.md with TDD requirements, PR workflow, and AI usage
  policy
- Add CODE_OF_CONDUCT.md based on Contributor Covenant
- Add SECURITY.md with vulnerability reporting scope and process
- Add AGENTS.md with AI usage policy for human contributors and AI
  agents
- Add CLAUDE.md to require reading AGENTS.md before any work
- Add Gitea issue templates for bug reports and feature requests
- Add pull request template with TDD and code quality checklist

.gitea/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,40 @@
+## Description
+
+<!-- Describe what this PR does and why. -->
+
+Closes #
+
+## Type of Change
+
+<!-- Remove lines that do not apply. -->
+
+- Bug fix (`fix/` branch)
+- New feature (`feature/` branch)
+- Documentation update
+- Other (please describe):
+
+## Checklist
+
+<!-- All boxes must be checked before requesting a review. -->
+
+### Branch & Scope
+- [ ] Branches from `develop` and targets `develop`
+- [ ] Covers a single topic (one feature or one fix)
+
+### Test-Driven Development
+- [ ] Failing tests were written before the implementation
+- [ ] All new code is covered by tests
+- [ ] `just test` passes locally
+
+### Code Quality
+- [ ] `just lint` passes with no warnings
+- [ ] `just format-check` passes
+- [ ] Code coverage has not dropped below 75%
+
+### AI Usage
+- [ ] No AI-generated code, **or** AI usage is disclosed below and
+      the majority of the code is human-authored
+
+## AI Usage Disclosure
+
+<!-- If AI was used, describe how. Delete this section if not applicable. -->