E3: add community health files

The repository had no contributor-facing documentation or automation
config. Add the standard set:

- CHANGELOG.md (Keep a Changelog format, 0.1.0-0.1.4 plus Unreleased)
- CONTRIBUTING.md (build/test steps, change standards, PolyForm-NC note)
- SECURITY.md (private reporting, supported versions)
- CODE_OF_CONDUCT.md (Contributor Covenant 2.1)
- .github/ISSUE_TEMPLATE (bug report, feature request, config)
- .github/PULL_REQUEST_TEMPLATE.md
- .github/dependabot.yml (cargo, npm, pip, github-actions — the last
  keeps the D1 SHA pins current)
- .github/CODEOWNERS

CODE_OF_CONDUCT.md

@@ -0,0 +1,47 @@
+# Code of Conduct
+
+## Our pledge
+
+We as members, contributors, and maintainers pledge to make participation in
+the Wickra project a respectful and welcoming experience for everyone,
+regardless of background or identity.
+
+## Our standards
+
+Behaviour that helps build a positive community includes:
+
+- Showing empathy and kindness toward others.
+- Respecting differing opinions, viewpoints, and experiences.
+- Giving and gracefully accepting constructive feedback.
+- Taking responsibility for mistakes and learning from them.
+- Focusing on what is best for the project and the community.
+
+Behaviour that is not acceptable includes:
+
+- Personal attacks, insults, or derogatory comments.
+- Harassment of any kind, public or private.
+- Publishing others' private information without explicit permission.
+- Other conduct that would reasonably be considered inappropriate in a
+  professional setting.
+
+## Scope
+
+This Code of Conduct applies in all project spaces — the repository, issues,
+pull requests, and discussions — and when an individual is representing the
+project in public spaces.
+
+## Enforcement
+
+Instances of unacceptable behaviour may be reported to the project maintainer
+at **kingchencp@gmail.com**. All reports will be reviewed and investigated
+promptly and fairly, and the maintainer will respect the privacy and security
+of the reporter.
+
+Maintainers may take any action they deem appropriate, including warnings,
+temporary bans, or permanent removal from the project, for behaviour that
+violates this Code of Conduct.
+
+## Attribution
+
+This Code of Conduct is adapted from the
+[Contributor Covenant](https://www.contributor-covenant.org), version 2.1.