Changes:
- Changed server port from 8000 to 6800 (in range 6500-6999 as requested)
- Updated all Docker Compose files (dev and prod)
- Updated all Dockerfiles (removed Cargo.lock dependency)
- Created backend/.dockerignore with Cargo.lock
- Added Cargo.lock to .gitignore (generated by cargo)
- Removed obsolete 'version' attribute from docker-compose files
- Updated all documentation to reflect new port:
* README.md
* thoughts/CONFIG.md
* thoughts/QUICKSTART.md
* thoughts/verification-report-phase-2.3.md
This fixes Docker build errors where Cargo.lock was not found during COPY operations.
Docker will now generate Cargo.lock during the build process as expected.
