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>

CONTRIBUTING.md

@@ -0,0 +1,42 @@
+# Contributing to temetro
+
+Thanks for your interest in contributing! temetro is an open-source clinical tool — contributions that improve reliability, usability, and data privacy are especially welcome.
+
+## Getting started
+
+1. Fork the repository and create a branch from `main`.
+2. Follow the setup steps in the root `README.md` to get the stack running locally.
+3. Make your changes, test them, and open a pull request.
+
+## Project structure
+
+This is a monorepo. Read the relevant `CLAUDE.md` before working in each area:
+
+- `frontend/` — Next.js chat UI (`frontend/CLAUDE.md`)
+- `backend/` — Express + Postgres API (`backend/CLAUDE.md`)
+
+Run `npm` commands from inside the relevant subdirectory, not the root.
+
+## Development workflow
+
+- **Branch naming:** `feat/...`, `fix/...`, `chore/...`, `docs/...`
+- **Commits:** one logical change per commit; prefix with `frontend:` or `backend:` when scoped
+- **PR size:** keep PRs focused — a feature and its tests, not a feature + unrelated cleanup
+
+## Code style
+
+- TypeScript throughout; no `any` without a comment explaining why
+- No dead code, no commented-out blocks
+- Comments only when the *why* is non-obvious
+
+## Reporting bugs
+
+Use the [bug report template](.github/ISSUE_TEMPLATE/bug_report.md). Include steps to reproduce and your environment.
+
+## Security issues
+
+Do **not** open a public issue for security vulnerabilities. See [SECURITY.md](SECURITY.md) for the responsible disclosure process.
+
+## Code of Conduct
+
+This project follows the [Contributor Covenant](CODE_OF_CONDUCT.md). By participating, you agree to uphold it.