Add comprehensive security and contribution documentation

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug Report
+about: Create a report to help us improve
+title: '[BUG] '
+labels: 'bug'
+assignees: ''
+---
+
+## Bug Description
+A clear and concise description of what the bug is.
+
+## To Reproduce
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+## Expected Behavior
+A clear and concise description of what you expected to happen.
+
+## Actual Behavior
+What actually happened instead.
+
+## Screenshots
+If applicable, add screenshots to help explain your problem.
+
+## Environment
+**Desktop/Server:**
+- OS: [e.g. Ubuntu 22.04, Windows 11, macOS 13]
+- Browser (if UI issue): [e.g. Chrome 120, Firefox 121]
+- Python Version: [e.g. 3.10.5]
+- Docker Version (if applicable): [e.g. 24.0.7]
+- DMARQ Version: [e.g. 0.1.0]
+
+**Deployment Method:**
+- [ ] Docker Compose
+- [ ] Manual Python installation
+- [ ] Other: _____
+
+## Configuration
+Relevant configuration (remove sensitive data):
+```yaml
+# docker-compose.yml excerpt or .env variables
+# DO NOT include passwords or secrets
+```
+
+## Logs
+```
+Paste relevant log output here
+```
+
+## Additional Context
+Add any other context about the problem here.
+
+## Possible Solution
+If you have suggestions on how to fix the issue, please describe them here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature Request
+about: Suggest an idea for DMARQ
+title: '[FEATURE] '
+labels: 'enhancement'
+assignees: ''
+---
+
+## Feature Description
+A clear and concise description of the feature you'd like to see.
+
+## Problem Statement
+Is your feature request related to a problem? Please describe.
+Ex. I'm always frustrated when [...]
+
+## Proposed Solution
+Describe the solution you'd like to see implemented.
+
+## Alternatives Considered
+Describe any alternative solutions or features you've considered.
+
+## Use Case
+Describe how this feature would be used and who would benefit from it.
+
+## Benefits
+- Benefit 1
+- Benefit 2
+- Benefit 3
+
+## Implementation Ideas
+If you have ideas about how this could be implemented, share them here.
+
+## Related Issues/PRs
+Link to any related issues or pull requests.
+
+## Mockups/Examples
+If applicable, add mockups, diagrams, or examples from other tools.
+
+## Additional Context
+Add any other context, screenshots, or information about the feature request here.
+
+## Checklist
+- [ ] I have searched existing issues to ensure this is not a duplicate
+- [ ] This feature aligns with DMARQ's mission of privacy-focused DMARC monitoring
+- [ ] I am willing to contribute to implementing this feature (optional)

.github/ISSUE_TEMPLATE/security_vulnerability.md

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+---
+name: Security Vulnerability
+about: Report a security issue (CONFIDENTIAL)
+title: '[SECURITY] '
+labels: 'security'
+assignees: ''
+---
+
+⚠️ **IMPORTANT: Do not create a public issue for serious security vulnerabilities**
+
+For serious security vulnerabilities, please email the maintainers directly instead of creating a public issue. See [SECURITY.md](../../SECURITY.md) for contact information.
+
+---
+
+## Security Issue Type
+- [ ] Authentication/Authorization issue
+- [ ] Data exposure
+- [ ] Injection vulnerability (SQL, XSS, etc.)
+- [ ] Cryptography issue
+- [ ] Dependency vulnerability
+- [ ] Configuration security
+- [ ] Other: _____
+
+## Affected Component
+- [ ] Backend API
+- [ ] Frontend/UI
+- [ ] Database
+- [ ] Docker configuration
+- [ ] Documentation
+- [ ] Dependencies
+
+## Severity Assessment
+- [ ] Critical (immediate action required)
+- [ ] High (significant risk)
+- [ ] Medium (moderate risk)
+- [ ] Low (minor risk)
+
+## Description
+Describe the security issue in detail.
+
+## Impact
+What is the potential impact of this vulnerability?
+
+## Steps to Reproduce
+Provide steps to reproduce the vulnerability.
+
+## Affected Versions
+Which versions of DMARQ are affected?
+
+## Suggested Remediation
+If you have suggestions for fixing the issue, provide them here.
+
+## References
+Links to similar vulnerabilities, CVEs, or relevant documentation.
+
+---
+
+**Remember**: For critical vulnerabilities, use private disclosure via email instead of public issues.