Fix Docker setup: Environment variables and file integration

[mvillmow]

This PR fixes the Docker setup to ensure the justfile, dockerfile, .env, and docker-compose.yml files work together properly.

Changes Made:

• .env: Fixed syntax issues with BUILD_UID, BUILD_GID, and GIT_COMMIT variables
• docker-compose.yml: Removed double dollar signs and added proper environment variable passing
• Dockerfile: Simplified user creation logic to avoid UID conflicts
• justfile: Added debug recipe for development workflow
• scripts/setup-env.sh: New script to automatically configure environment variables

Result:

• Building debug mode...
  -- Fetching GTest with GMock from GitHub...
  -- Google Benchmark not found, fetching from GitHub...
  -- Failed to find LLVM FileCheck
  -- git version: v1.8.3 normalized to 1.8.3
  -- Google Benchmark version: 1.8.3
  -- Enabling additional flags: -DINCLUDE_DIRECTORIES=/workspace/build/debug/_deps/benchmark-src/include
  -- Performing Test HAVE_THREAD_SAFETY_ATTRIBUTES -- success
  -- Performing Test HAVE_STD_REGEX -- success
  -- Performing Test HAVE_GNU_POSIX_REGEX -- failed to compile
  -- Performing Test HAVE_POSIX_REGEX -- success
  -- Performing Test HAVE_STEADY_CLOCK -- success
  -- Performing Test HAVE_PTHREAD_AFFINITY -- success
  -- Cista fuzzing enabled
  -- Build spdlog: 1.12.0
  -- Build type: Debug
  -- gRPC support disabled. Use -DENABLE_GRPC=ON to enable Phase 8 distributed features
  -- Profiling tests disabled. Use -DENABLE_PROFILING=ON to enable.
  -- Workflow examples disabled. Use -DBUILD_EXAMPLES=ON to enable.
  -- Configuring done (0.6s)
  -- Generating done (0.0s)
  -- Build files have been written to: /workspace/build/debug
  ninja: no work to do.
  ✓ Debug build complete: build/debug/ now works correctly
• Starting development container for debugging... builds and enters development container
• All environment variables (BUILD_UID, BUILD_GID, GIT_COMMIT) are properly set
• Docker containers run with correct user permissions

Resolves Docker build issues and ensures proper user permissions in containers.