chore: add community health files

Add MIT LICENSE (root, backend, frontend), CONTRIBUTING.md, CODE_OF_CONDUCT.md,
SECURITY.md, GitHub issue templates (bug/feature), and PR template.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Report a problem with temetro
+labels: bug
+---
+
+**Describe the bug**
+A clear description of what the bug is.
+
+**To reproduce**
+Steps to reproduce the behavior:
+1. 
+2. 
+3. 
+
+**Expected behavior**
+What you expected to happen.
+
+**Actual behavior**
+What actually happened.
+
+**Environment**
+- OS: 
+- Browser (if frontend): 
+- Node version: 
+- Are you running via Docker or local dev?
+
+**Screenshots / logs**
+If applicable, add screenshots or relevant log output.
+
+**Additional context**
+Any other context about the problem.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: Suggest an idea or improvement for temetro
+labels: enhancement
+---
+
+**Is your feature request related to a problem?**
+A clear description of the problem. e.g. "I'm frustrated when..."
+
+**Describe the solution you'd like**
+A clear description of what you want to happen.
+
+**Which part of the project does this affect?**
+- [ ] Frontend (Next.js chat UI)
+- [ ] Backend (API / auth / database)
+- [ ] Both
+
+**Alternatives considered**
+Any alternative solutions or features you've considered.
+
+**Additional context**
+Any other context, mockups, or screenshots.

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+<!-- What does this PR do? One or two sentences. -->
+
+## Type of change
+
+- [ ] Bug fix
+- [ ] New feature
+- [ ] Refactor / cleanup
+- [ ] Docs
+- [ ] Chore / tooling
+
+## Testing
+
+<!-- How did you verify this works? -->
+
+## Checklist
+
+- [ ] I've tested the affected path manually
+- [ ] No `.env` secrets are committed
+- [ ] Relevant docs updated (see `../temetro/docs` if needed)