Add repository agent guide

AGENTS.md

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+# Robot U Site Agent Guide
+
+## Purpose
+
+This repository contains the Robot U community site.
+
+It is a thin application layer over Forgejo:
+
+- Forgejo is the source of truth for authentication, public content repos, and issue-backed discussions.
+- This app provides the web UI, course/lesson browsing, markdown rendering, and ICS calendar ingestion.
+- The current live Forgejo instance is `https://aksal.cloud`.
+
+## Stack
+
+- Backend: FastAPI
+- Frontend: Preact + TypeScript + Vite
+- Python tooling: `uv`, `ruff`
+- Frontend tooling: `bun`, Biome
+
+## Important Files
+
+- `app.py`: FastAPI app and SPA/static serving
+- `live_prototype.py`: live payload assembly for courses, lessons, discussions, and events
+- `forgejo_client.py`: Forgejo API client
+- `calendar_feeds.py`: ICS/webcal feed loading and parsing
+- `settings.py`: env-driven runtime settings
+- `frontend/src/App.tsx`: client routes and page composition
+- `frontend/src/MarkdownContent.tsx`: safe markdown renderer used in lessons and discussions
+- `scripts/start.sh`: main startup command for local runs
+
+## Repo Layout Notes
+
+- The root repository is the site application.
+- `examples/quadrature-encoder-course/` is a separate nested git repo used as sample content. It is intentionally ignored by the root repo and should stay that way.
+
+## First-Time Setup
+
+### Python
+
+```bash
+python3 -m venv .venv
+.venv/bin/pip install -r requirements.txt
+```
+
+### Frontend
+
+```bash
+cd frontend
+~/.bun/bin/bun install
+```
+
+## Environment
+
+Runtime configuration is loaded from shell env, then `.env`, then `.env.local` through `scripts/start.sh`.
+
+Recommended local flow:
+
+```bash
+cp .env.example .env
+```
+
+Useful variables:
+
+- `FORGEJO_BASE_URL=https://aksal.cloud`
+- `FORGEJO_TOKEN=...`
+- `CALENDAR_FEED_URLS=webcal://...`
+- `HOST=0.0.0.0`
+- `PORT=8800`
+
+Notes:
+
+- `FORGEJO_TOKEN` is required for live repo and discussion reads on `aksal.cloud`.
+- `CALENDAR_FEED_URLS` is optional and accepts comma-separated `webcal://` or `https://` ICS feeds.
+- Do not commit `.env` or `.env.local`.
+
+## Main Start Command
+
+Use this for the normal local app flow:
+
+```bash
+./scripts/start.sh
+```
+
+What it does:
+
+1. Loads `.env` and `.env.local` if present.
+2. Builds the frontend with `bun`.
+3. Starts FastAPI with `uvicorn`.
+
+Override host/port when needed:
+
+```bash
+HOST=0.0.0.0 PORT=8800 ./scripts/start.sh
+```
+
+## Development Commands
+
+### Backend only
+
+```bash
+.venv/bin/python -m uvicorn app:app --reload
+```
+
+### Frontend only
+
+```bash
+cd frontend
+~/.bun/bin/bun run dev
+```
+
+### Frontend production build
+
+```bash
+cd frontend
+~/.bun/bin/bun run build
+```
+
+## Quality Checks
+
+Run both before pushing:
+
+```bash
+./scripts/check_python_quality.sh
+./scripts/check_frontend_quality.sh
+```
+
+## Product/Data Model Background
+
+- Public non-fork repos are scanned.
+- A repo with `/lessons/` is treated as a course repo.
+- A repo with `/blogs/` is treated as a post repo.
+- Lessons are discovered from `lessons/<chapter>/<lesson>/`.
+- Each lesson folder is expected to contain one markdown file plus optional assets.
+- Frontmatter is used when present for `title` and `summary`.
+- Discussions are loaded from Forgejo issues and comments.
+- Calendar events are loaded from ICS feeds, not managed in-app.
+
+## UI Expectations
+
+- The UI should not expose Forgejo as a user-facing implementation detail unless necessary for debugging.
+- Course cards should open course pages.
+- Lesson rows should open lesson pages.
+- Discussion pages should focus on one thread at a time.
+- Markdown should render as readable content, not raw source.
+
+## Push Workflow
+
+The site source repo currently lives at:
+
+- `git@aksal.cloud:Robot-U/robot-u-site.git`
+
+Typical push flow:
+
+```bash
+git status
+git add ...
+git commit -m "..."
+git push origin main
+```