chore: add GitHub community files and CI pipeline

- .github/workflows/ci.yml: TypeScript check + Vitest + build on every PR
- .github/dependabot.yml: weekly npm + Actions updates (minor/patch grouped)
- .github/ISSUE_TEMPLATE/: bug_report, feature_request, config (→ Discussions)
- .github/PULL_REQUEST_TEMPLATE.md: checklist for contributors
- SECURITY.md: responsible disclosure policy via GitHub Advisories
- CONTRIBUTING.md: dev setup, code style, commit conventions

CONTRIBUTING.md

@@ -0,0 +1,68 @@
+# Contributing to Immich Folio
+
+Thanks for your interest in contributing! 🎉
+
+## Ways to contribute
+
+- **Bug reports** — [Open a bug report issue](https://github.com/ralksta/immich-folio/issues/new?template=bug_report.md)
+- **Feature requests** — [Open a feature request](https://github.com/ralksta/immich-folio/issues/new?template=feature_request.md)
+- **Pull requests** — see below
+- **Discussions** — [Ask questions or share ideas](https://github.com/ralksta/immich-folio/discussions)
+
+## Development setup
+
+```bash
+# 1. Clone
+git clone https://github.com/ralksta/immich-folio.git
+cd immich-folio
+
+# 2. Install
+npm install
+
+# 3. Configure
+cp content/gallery.example.yaml content/gallery.yaml
+# Edit .env or set IMMICH_URL + IMMICH_API_KEY
+
+# 4. Run
+npm run dev       # http://localhost:3000
+npm run build     # production build check
+```
+
+## Before submitting a PR
+
+```bash
+npx tsc --noEmit   # must be 0 errors
+npx vitest run     # all tests must pass
+npm run build      # build must succeed
+```
+
+## Code style
+
+- **TypeScript** — strict mode, no `any` without justification
+- **Components** — Server Components by default; use `'use client'` only when necessary
+- **CSS** — vanilla CSS variables, no Tailwind, no CSS-in-JS
+- **Naming** — descriptive names, no abbreviations in public APIs
+
+## Commit messages
+
+Use [Conventional Commits](https://www.conventionalcommits.org/):
+
+```
+feat: add new hero style
+fix: correct image aspect ratio on mobile
+security: escape HTML in map popups
+docs: update theming guide
+chore: bump next to 15.x
+```
+
+## Pull Request checklist
+
+- [ ] `npx tsc --noEmit` passes
+- [ ] `npx vitest run` passes
+- [ ] `npm run build` passes
+- [ ] No secrets in the diff
+- [ ] Documentation updated if needed
+
+## License
+
+By contributing, you agree that your contributions will be licensed under the [MIT License](LICENSE).