rebuild dev and build system with single marp server

- simplify development: single marp server on port 3000 instead of 3 processes
- rename klausur to klausurfolien for better naming
- update extract script to use 00-intro.md as template when no 01-*.md exists
- update makefile and package.json for new workflow
- add comprehensive AGENTS.md guidelines

README.md

@@ -27,10 +27,12 @@ build/                # Generated output (gitignored)
 ## Development
 
 ```bash
-# Start dev servers (hot reload)
-make dev              # All courses + index
-make dev-b            # 223015b only (port 1311)
-make dev-c            # 223015c only (port 1312)
+# Start development server (hot reload)
+make dev              # Single server for all courses (port 3000)
+
+# Access individual courses:
+# 223015b: http://localhost:3000/223015b/
+# 223015c: http://localhost:3000/223015c/
 ```
 
 ## Build
@@ -43,7 +45,7 @@ make html             # HTML only
 make pdf              # PDF only
 ```
 
-## Klausur Slides
+## Klausur Folien
 
 Extract exam-relevant slides (marked with `<!-- _class: klausur -->`) into a single file:
 
@@ -53,7 +55,7 @@ make klausur-b        # 223015b only
 make klausur-c        # 223015c only
 ```
 
-Output: `slides/<course>/klausur.md`
+Output: `slides/<course>/klausurfolien.md`
 
 The generated file includes:
 - A title slide per kapitel for orientation