add GH PR/issue templates (#74)

Author: monrax

.github/ISSUE_TEMPLATE.md

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+## Summary
+
+Give a brief description of the problem.
+
+### Details
+
+Explain with further technical details, if applies.
+
+### Impact
+
+Why is it important?
+
+## How to reproduce?
+
+### Environment
+- Helm chart version:
+- Graylog version:
+- Kubernetes version:
+- Cloud provider / platform:
+
+### Pre-flight checks
+- [ ] `helm lint ./graylog` passes
+- [ ] Checked existing issues for duplicates
+
+### Steps
+1. ...
+2. ...
+
+## Notes for maintainers
+_Any additional context, logs, or screenshots_

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+Short description of the change.
+
+## What changed
+- List of meaningful changes
+
+## Checklist
+- [ ] Tests added/updated
+- [ ] Documentation updated
+- [ ] This PR includes a new feature
+- [ ] This PR includes a bugfix
+- [ ] This PR includes a refactor
+
+## Testing Checklist
+
+### Static Validation
+- [ ] `helm lint ./graylog` passes
+- [ ] `helm template graylog ./graylog --validate` passes
+
+### Installation
+- [ ] Fresh installation completes successfully
+- [ ] All pods reach Running state
+- [ ] `helm test graylog -n graylog` passes
+
+### Functional (if applicable)
+- [ ] Web UI accessible and login works
+- [ ] DataNodes visible in System > Data Nodes
+- [ ] Inputs can be created and receive data
+
+### Upgrade (if applicable)
+- [ ] Upgrade from previous release succeeds
+- [ ] Scaling up/down works correctly
+- [ ] Configuration changes apply correctly
+
+### Specific to this PR
+- [ ] _describe what was specifically tested_
+
+## Notes for reviewers
+- [ ] Verify all tests pass
+- [ ] Sync up with the author before merging
+- [ ] The commit history must be preserved - please use the rebase-merge or standard merge options