restructure: rename termin to kapitel, flatten folder structure

- rename slide files: YYYY-MM-DD-termin-N-topic.md → NN-topic.md
- flatten folders: courses/X/slides/ → slides/X/
- replace "Termin" with "Kapitel" in all content
- add klausur extraction script (make klausur)
- update Makefile, generate-index.sh, dev-server.sh
- add README.md with full documentation

scripts/extract-klausur.sh

@@ -0,0 +1,112 @@
+#!/usr/bin/env bash
+# Extract klausur-relevant slides from all kapitel
+# Usage: ./extract-klausur.sh <course_id>
+# Output: slides/<course>/klausur.md
+
+set -e
+
+COURSE="${1:-223015b}"
+SLIDES_DIR="slides/$COURSE"
+OUTPUT_FILE="$SLIDES_DIR/klausur.md"
+
+# Find the first kapitel file (01-*.md) to copy styles from
+FIRST_KAPITEL=$(ls "$SLIDES_DIR"/01-*.md 2>/dev/null | head -1)
+
+if [[ -z "$FIRST_KAPITEL" ]]; then
+  echo "Error: No 01-*.md file found in $SLIDES_DIR"
+  exit 1
+fi
+
+echo "Extracting klausur slides for $COURSE..."
+
+# Extract frontmatter and styles (everything up to first <!-- _class: line after style block)
+# This gets the YAML frontmatter + <style> block
+awk '
+  BEGIN { in_frontmatter = 0; in_style = 0; done = 0 }
+  /^---$/ && !in_frontmatter { in_frontmatter = 1; print; next }
+  /^---$/ && in_frontmatter && !in_style { in_frontmatter = 0; print; next }
+  in_frontmatter { print; next }
+  /<style>/ { in_style = 1; print; next }
+  /<\/style>/ { in_style = 0; print; print ""; done = 1; next }
+  in_style { print; next }
+  done { exit }
+' "$FIRST_KAPITEL" > "$OUTPUT_FILE"
+
+# Add warning comment
+cat >> "$OUTPUT_FILE" << 'EOF'
+<!--
+  ╔═══════════════════════════════════════════════════════════════════╗
+  ║  AUTO-GENERATED FILE - DO NOT EDIT MANUALLY                       ║
+  ║                                                                   ║
+  ║  This file is generated by: make klausur                          ║
+  ║  Source: scripts/extract-klausur.sh                               ║
+  ║                                                                   ║
+  ║  To update, edit the source slides and re-run make klausur        ║
+  ╚═══════════════════════════════════════════════════════════════════╝
+-->
+
+EOF
+
+# Extract and copy the cover slide (first slide after frontmatter/styles, up to first ---)
+awk '
+  BEGIN { past_style = 0; in_cover = 0; printed = 0 }
+  /<\/style>/ { past_style = 1; next }
+  past_style && !in_cover && /^[^[:space:]]/ { in_cover = 1 }
+  in_cover && /^---$/ { print "---\n"; exit }
+  in_cover { print }
+' "$FIRST_KAPITEL" >> "$OUTPUT_FILE"
+
+# Process each kapitel file in order - extract klausur slides only
+for md_file in $(ls "$SLIDES_DIR"/[0-9][0-9]-*.md 2>/dev/null | grep -v klausur | sort); do
+  filename=$(basename "$md_file")
+  kapitel_num=$(echo "$filename" | grep -oE '^[0-9]+' | sed 's/^0*//')
+
+  # Skip intro (kapitel 0)
+  if [[ "$kapitel_num" == "0" ]] || [[ -z "$kapitel_num" ]]; then
+    continue
+  fi
+
+  # Check if file has any klausur slides
+  if ! grep -q '<!-- _class: klausur -->' "$md_file"; then
+    continue
+  fi
+
+  echo "  Processing Kapitel $kapitel_num..."
+
+  # Extract klausur slides, hide header/footer, convert * to - bullets
+  awk '
+    /<!-- _class: klausur -->/ {
+      in_klausur = 1
+      # Add header/footer hiding
+      print "<!-- _header: \"\" -->"
+      print "<!-- _footer: \"\" -->"
+      print ""
+      next
+    }
+    in_klausur && /^---$/ {
+      print "\n---\n"
+      in_klausur = 0
+      next
+    }
+    in_klausur {
+      # Skip marp directives (we add our own)
+      if (/<!-- _header:/ || /<!-- _footer:/ || /<!-- _backgroundColor:/) next
+      # Convert * bullets to - bullets (avoid fragments)
+      gsub(/^\* /, "- ")
+      gsub(/^  \* /, "  - ")
+      gsub(/^    \* /, "    - ")
+      print
+    }
+  ' "$md_file" >> "$OUTPUT_FILE"
+
+done
+
+# Remove trailing --- and empty lines
+perl -i -0777 -pe 's/\n*---\n*$/\n/' "$OUTPUT_FILE"
+
+# Count slides
+slide_count=$(grep -c '^---$' "$OUTPUT_FILE" 2>/dev/null || echo "0")
+
+echo ""
+echo "Generated: $OUTPUT_FILE"
+echo "Total slides: $slide_count"