docs: add governance, support, DCO and security assurance case (#164)

Add GOVERNANCE.md, MAINTAINERS.md, SUPPORT.md, DCO; add a DCO sign-off requirement to CONTRIBUTING.md and a security assurance case to SECURITY.md. Closes OpenSSF Silver / OSPS Baseline documentation gaps. Additive only.

SUPPORT.md

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+# Support
+
+Thanks for using Wickra! Here is where to get help, depending on what you need.
+
+## Documentation first
+
+Most questions are answered in the documentation:
+
+- **Docs site:** <https://docs.wickra.org> — quickstarts for Rust, Python,
+  Node.js and WebAssembly, a per-indicator reference, warmup periods, the data
+  layer, and an FAQ.
+- **README:** <https://github.com/wickra-lib/wickra#readme> — installation and a
+  quick overview.
+- **API docs (Rust):** <https://docs.rs/wickra>.
+
+## Questions and help
+
+- Ask a question with the
+  [question issue template](.github/ISSUE_TEMPLATE/question.md).
+- Browse [existing issues](https://github.com/wickra-lib/wickra/issues) — your
+  question may already be answered.
+
+## Bugs and feature requests
+
+- **Bugs:** use the bug-report issue template.
+- **Feature requests / new indicators:** use the feature-request template.
+
+## Security issues
+
+Please do **not** report security vulnerabilities through public issues. Follow
+the process in [`SECURITY.md`](SECURITY.md) (private GitHub advisory or email).
+
+## Support expectations
+
+Wickra is maintained by a single maintainer on a best-effort basis. Issues are
+triaged and acknowledged as time allows; there is no commercial support or SLA.
+Clear, reproducible reports get help fastest.