docs: add contributing guide for Devoter API

CONTRIBUTING.md

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+# Contributing to Devoter API
+
+Thank you for your interest in contributing to Devoter API! This guide explains how to set up your environment, make changes, and submit pull requests in a consistent and high‑quality manner.
+
+Please also review our community guidelines:
+
+- Code of Conduct: see `CODE_OF_CONDUCT.md` in this repository.
+
+---
+
+## Ways to Contribute
+
+- Report bugs and propose enhancements
+- Improve documentation (including files under `docs/`)
+- Add tests to increase coverage and guard against regressions
+- Implement new features and fix issues
+
+For larger changes, open an issue to discuss the approach before starting.
+
+---
+
+## Development Setup
+
+### Prerequisites
+
+- Node.js 18+
+- pnpm (recommended) or npm/yarn
+- A database compatible with the Prisma schema (commonly PostgreSQL)
+
+### 1) Fork and clone the repo
+
+```bash
+# Replace <your-user> with your GitHub username
+git clone https://github.com/<your-user>/devoter-api.git
+cd devoter-api
+```
+
+### 2) Install dependencies
+
+```bash
+pnpm install
+# or: npm install / yarn install
+```
+
+### 3) Environment variables
+
+Create a local `.env` file with the variables required by the app. Typical keys include:
+
+- `PORT` (default: 3000)
+- `HOST` (default: localhost)
+- `CORS_ORIGIN` (default: http://localhost:3000)
+- `DATABASE_URL` (Prisma connection string)
+- optional: `NODE_ENV` (development | production)
+
+### 4) Prisma database setup
+
+Generate Prisma Client and apply pending migrations to your dev database:
+
+```bash
+pnpm exec prisma generate
+pnpm exec prisma migrate dev
+```
+
+You can inspect data with Prisma Studio:
+
+```bash
+pnpm exec prisma studio
+```
+
+### 5) Run the app in development
+
+```bash
+pnpm dev
+```
+
+The server will start on `http://localhost:3000` by default.
+
+### 6) Build for production
+
+```bash
+pnpm build
+```
+
+### 7) Tests
+
+This project uses Vitest.
+
+```bash
+# Run the test suite
+pnpm test
+
+# Run with coverage
+pnpm test:coverage
+```
+
+---
+
+## Project Conventions
+
+- Language: TypeScript (strict)
+- Framework: Fastify 5
+- Validation: `@sinclair/typebox`
+- Rate limiting: see `src/middleware/rateLimit.ts`
+- Error handling: see `src/plugins/errorPlugin.ts` and `src/utils/errorHandler.ts`
+- Auth / signature verification: see `src/middleware/auth.ts` and `src/utils/verifySignature.ts`
+
+General guidelines:
+
+- Favor small, focused modules and Fastify plugins
+- Use async/await and handle errors with the provided helpers
+- Define schemas for request/response on routes
+- Keep functions small and add tests
+
+Documentation:
+
+- Update `docs/` when behavior, error handling, or rate limits change
+- Keep `README.md` in sync for notable developer‑facing changes
+
+---
+
+## Git and Branching
+
+We follow a lightweight GitHub Flow.
+
+- Branch from `main`
+- Use descriptive branch names: `<type>/<short-description>`
+  - Examples: `feat/register-endpoint`, `fix/invalid-port`, `docs/update-rate-limits`
+- Use clear commit messages (Conventional Commits recommended):
+  - `feat: add registration route with wallet signature verification`
+  - `fix: validate PORT env var and fail fast`
+  - `docs: document error handling strategy`
+
+---
+
+## Pull Requests
+
+Before opening a PR, please ensure:
+
+- The code compiles and type‑checks: `pnpm build`
+- Tests are added/updated and passing: `pnpm test`
+- Relevant docs are updated if behavior or APIs changed
+- Prisma migrations are included if the schema changed
+- The PR description explains the problem, solution, and any trade‑offs
+
+PR checklist:
+
+- [ ] Build succeeds (no TypeScript errors)
+- [ ] Tests passing (and new tests added if applicable)
+- [ ] Documentation updated (if applicable)
+- [ ] Small, focused changes (no unrelated diffs)
+
+Maintainers will review your PR and may request changes. Please be responsive to feedback.
+
+---
+
+## Reporting Issues
+
+When filing an issue, include:
+
+- Expected vs. actual behavior
+- Steps to reproduce (ideally minimal and deterministic)
+- Logs/error messages (redact secrets)
+- Environment details (OS, Node.js version, database)
+- Any relevant configs or payloads
+
+---
+
+## Security
+
+If you discover a security vulnerability, do not open a public issue. Please report it privately (e.g., via GitHub Security Advisories) so we can coordinate a fix and disclosure.
+
+---
+
+## License
+
+By contributing, you agree that your contributions will be licensed under the same license specified in `package.json`.
+
+Thanks for helping improve Devoter API!