Add local development environment setup (Gemfile, AGENTS.md)

AGENTS.md

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+# AGENTS.md
+
+## Cursor Cloud specific instructions
+
+This is a **Jekyll-powered GitHub Pages** static site hosting university course slides for AI-related courses. There is no application backend, database, or build pipeline.
+
+### Tech Stack
+- **Jekyll** (via `github-pages` gem) renders Markdown into HTML
+- **Theme**: `jekyll-theme-cayman` (configured in `_config.yml`)
+- **Content**: Markdown files (`.md`) + PDF/PPTX lecture slides + images
+
+### Running the dev server
+
+```bash
+bundle exec jekyll serve --host 0.0.0.0 --port 4000
+```
+
+Site available at `http://localhost:4000/`. Auto-regeneration is enabled — editing `.md` files triggers a rebuild automatically.
+
+### Key gotchas
+
+- **No front matter required**: The `github-pages` gem includes `jekyll-optional-front-matter`, so `.md` files render without `---` YAML front matter. Standard Jekyll (without `github-pages` gem) would NOT process these files.
+- **Sass deprecation warnings** from the upstream `jekyll-theme-cayman` are expected and harmless.
+- **"No GitHub API authentication" warning** during `jekyll serve` is normal for local development and does not affect site rendering.
+- The `_config.yml` must NOT be modified for local dev compatibility — the `Gemfile` and `github-pages` gem handle GitHub Pages parity.
+
+### Testing
+
+There are no automated tests. Verification is manual: run the dev server and confirm pages render correctly in a browser.
+
+### Lint
+
+No linter is configured for this project.

Gemfile

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+source "https://rubygems.org"
+
+gem "github-pages", group: :jekyll_plugins
+gem "webrick"