add documentation

- README.md: project overview, commands, structure
- CLAUDE.md: agent guidelines for slide editing

CLAUDE.md

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+# CLAUDE.md - Agent Guidelines for HdM Slides
+
+This project builds presentation decks for Marp, supporting multiple courses.
+
+## Courses
+
+- **223015b** - Dateiformate, Schnittstellen, Speichermedien (6 Termine)
+- **223015c** - Internettechnologien (3 Termine)
+
+## Agent Restrictions
+
+- Agent NEVER runs commands outside this folder
+- Agent NEVER runs build/deploy commands without explicit user request
+- Agent NEVER runs deploy commands (make deploy, scp, etc.) without explicit user permission
+
+## Critical File Protection
+
+Slide files in `courses/*/slides/*.md` are main content files:
+- ALLOWED: Adding slides, adjusting content, fixing typos, enhancing sections
+- FORBIDDEN (without permission): Deleting slides, removing sections, bulk deletions
+- Before ANY deletion: ALWAYS ask user for confirmation
+
+## Project Structure
+
+```
+courses/
+├── 223015b/slides/     # Dateiformate course
+└── 223015c/slides/     # Internettechnik course
+scripts/                # Shared scripts
+themes/                 # Custom Marp themes
+build/                  # Generated output (gitignored)
+```
+
+## Build Commands
+
+```bash
+make dev-b          # Dev server 223015b (port 1312)
+make dev-c          # Dev server 223015c (port 1313)
+make build          # Build all courses
+make build-b        # Build 223015b only
+make build-c        # Build 223015c only
+make html           # HTML only
+make pdf            # PDF only
+make deploy         # Deploy all (ASK FIRST!)
+```
+
+## Nix Flake Commands
+
+```bash
+nix develop                           # Dev shell with all tools
+nix run .#qr -- "https://example.com" # Generate QR code
+nix run .#qr-slides -- 223015b        # QR for course
+nix run .#optimize-img -- <path>      # Optimize images
+```
+
+## Code Style Guidelines
+
+### File Structure
+- Slides in `courses/<course>/slides/`
+- Assets in `courses/<course>/slides/assets/`
+- Always reference images as `./assets/filename.png`
+
+### Naming Conventions
+- Slide files: `YYYY-MM-DD-termin-N-topic.md`
+- Images: `snake_case.jpg` or `kebab-case.jpg`
+
+### Markdown Style
+- Use ATX-style headers (# ## ###)
+- Frontmatter for slide metadata
+- Never include a final `---` (creates empty slide)
+
+### Git Workflow
+- Commit messages: ALWAYS lowercase
+- NEVER add co-authoring lines or generated footers