Add step 03: Docker, Deployment & First Live App

- Introduced a new section on building Docker images and deploying the fitness app.
- Added detailed explanations of Docker concepts, including images, containers, and volumes.
- Included three Dockerfiles for the backend and frontend, with line-by-line explanations.
- Updated main.tex to include step_03.tex.
- Modified main.toc to reflect new sections and subsections.
- Updated main.fls and main.log to include new font inputs and log entries related to the new content.
- Adjusted font configurations for FiraMono and FiraSans in main.fls.
- Updated PDF and synctex files to reflect changes in the document structure.

LateX/main.tex

@@ -245,6 +245,7 @@
 % ============================================
 \input{step_01.tex} 
 \input{step_02.tex} 
+\input{step_03.tex} 
 
 % Weitere Kapitel folgen hier:
 % \input{step_02.tex}