chore: add open-source governance files (GPLv3 + contributing docs)

Add standard open-source project files:
- LICENSE.md — GNU GPL v3.0 or later (verbatim)
- CONTRIBUTING.md — setup, workflow, and required AI-usage disclosure
- CONTRIBUTORS.md — maintainers, contributors, AI-assistance policy
- CODE_OF_CONDUCT.md — Contributor Covenant 2.1
- SECURITY.md — private vulnerability reporting
- .gitea/ISSUE_TEMPLATE/* + PULL_REQUEST_TEMPLATE.md
- README: License section (Copyright (C) 2026 Runic Gateway)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XmHdsbnLzDMAVQkAoTQSBe

CONTRIBUTING.md

@@ -0,0 +1,94 @@
+# Contributing to Runic Gateway — Website
+
+Thanks for your interest in contributing! This repo is the full-stack website
+(Node.js + Express API, MariaDB, React + Vite SPA). This guide covers how to get
+set up, the workflow we follow, and the rules for contributions.
+
+By participating you agree to abide by our
+[Code of Conduct](CODE_OF_CONDUCT.md).
+
+## Ways to contribute
+
+- **Report a bug** or **request a feature** through the
+  [issue tracker](https://gitea.whitlocktech.com/RunicGateway/website/issues)
+  (issue templates are provided).
+- **Improve the code or docs** by opening a pull request (see below).
+- **Never** report a security vulnerability in a public issue — see
+  [SECURITY.md](SECURITY.md).
+
+## Development setup
+
+**Prerequisites:** Node.js 20+ and npm, plus Docker (for MariaDB).
+
+The [README](README.md) has the full setup guide. The short version for local
+development with hot reload:
+
+```bash
+# 1. Start a MariaDB the backend can reach
+docker run -d --name rg-db -p 3306:3306 \
+  -e MARIADB_DATABASE=runic_gateway -e MARIADB_USER=runic \
+  -e MARIADB_PASSWORD=devpass -e MARIADB_ROOT_PASSWORD=rootpass mariadb:11
+
+# 2. Backend (terminal 1)
+cp server/.env.example server/.env   # set DB_* , JWT_SECRET, ADMIN_USERNAME/PASSWORD
+npm run install-all
+npm run server                       # nodemon -> http://localhost:3000
+
+# 3. Frontend (terminal 2)
+npm run client                       # Vite -> http://localhost:5173
+```
+
+Develop against **http://localhost:5173** (the Vite dev server proxies `/api`).
+
+### Tests & checks
+
+Please run the server test suite and make sure the client builds before opening
+a PR — these are the same checks CI runs on your PR:
+
+```bash
+npm test            # server tests
+npm run build       # client production build
+```
+
+If you add or change an API route, regenerate the Swagger spec
+(`cd server && npm run swagger`) and commit the updated
+`server/swagger/swagger-output.json`.
+
+## Branch & PR workflow
+
+1. Fork or branch from `main`. Use a descriptive branch name
+   (`feature/…`, `fix/…`, `docs/…`, `chore/…`).
+2. Keep changes focused; small PRs are easier to review.
+3. Push and open a pull request against `main`. Fill out the PR template,
+   including the **AI-assisted contributions** disclosure.
+4. Make sure PR checks (server tests + client build) are green.
+5. A maintainer will review; address feedback by pushing follow-up commits.
+
+### Commit messages
+
+We use [Conventional Commits](https://www.conventionalcommits.org/) —
+`type(scope): summary` (e.g. `feat(auth): add TOTP challenge step`,
+`fix(brand): link footer badge to Gitea org`). Common types: `feat`, `fix`,
+`docs`, `chore`, `refactor`, `test`, `ci`.
+
+## AI-assisted contributions (disclosure required)
+
+This project is developed openly with AI assistance, and we ask the same
+transparency of everyone. **If you used an AI tool** (Claude, Copilot, ChatGPT,
+Cursor, etc.) to help produce a contribution, you must disclose it:
+
+- Tick the AI-usage box in the pull-request template and name the tool(s).
+- Mark AI-authored commits with a trailer, e.g.
+  `Co-Authored-By: Claude <noreply@anthropic.com>` or `Assisted-By: <tool>`.
+- You remain responsible for every line you submit: review it, understand it,
+  and make sure it is correct and that you have the right to contribute it.
+
+Disclosed AI assistance is welcome. Undisclosed AI-generated contributions are
+not, and may be closed.
+
+## License
+
+Runic Gateway is licensed under the **GNU General Public License v3.0 or later**
+(see [LICENSE.md](LICENSE.md)). By submitting a contribution you agree that it is
+licensed under the same terms (inbound = outbound) and that you have the right to
+contribute it.