Config: Change server port to 6800 and remove Cargo.lock dependency

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.

backend/docker/Dockerfile

@@ -1,7 +1,7 @@
 FROM rust:1.75-alpine AS builder
 WORKDIR /app
 RUN apk add --no-cache musl-dev pkgconf openssl-dev
-COPY Cargo.toml Cargo.lock ./
+COPY Cargo.toml ./
 RUN mkdir src && echo 'fn main() {}' > src/main.rs
 RUN cargo build --release && rm -rf src
 COPY src ./src

backend/docker/Dockerfile.dev

@@ -2,7 +2,7 @@ FROM rust:1.75-alpine
 WORKDIR /app
 RUN apk add --no-cache musl-dev pkgconf openssl-dev curl wget git pkgconfig
 RUN cargo install cargo-watch
-COPY Cargo.toml Cargo.lock ./
+COPY Cargo.toml ./
 RUN mkdir src && echo 'fn main() {}' > src/main.rs
 RUN cargo build && rm -rf src
 COPY src ./src