chore: add coc, contibution, and security documents for community guidelines (#31)

.github/PULL_REQUEST_TEMPLATE.md

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+## Description
+
+<!-- describe what this PR does -->
+
+## Related Issues
+
+<!-- link any related issues: fixes #123, closes #456 -->
+
+## Type of Change
+
+- [ ] bug fix
+- [ ] new feature
+- [ ] breaking change
+- [ ] documentation
+- [ ] refactoring
+- [ ] other: <!-- describe -->
+
+## AI Disclosure
+
+<!-- required: select one -->
+
+- [ ] `ai: none` — no ai assistance used
+- [ ] `ai: assisted` — ai helped with portions (describe below)
+- [ ] `ai: generated` — significant portions were ai-generated (describe below)
+
+<!-- if ai-assisted or ai-generated, briefly describe what was ai-generated: -->
+
+## Checklist
+
+- [ ] i have tested these changes locally
+- [ ] i have run `make test` and all tests pass
+- [ ] i have run `make lint` and fixed any issues
+- [ ] i have updated documentation if needed
+- [ ] my code follows the existing style of the project
+
+## Screenshots / Terminal Output
+
+<!-- if applicable, add screenshots or terminal output showing the change -->
+