build(dev): add live development environment with cargo-watch

[mtsz-pl]

build(dev): add live development environment with cargo-watch

• Add Dockerfile.dev with cargo-watch for automatic recompilation on file changes
• Configure compose.dev.yaml with read-only volume mounts for source code
• Use Docker volumes for build artifacts to keep host filesystem clean
• Enable RUST_LOG=debug for development logging
• Update comment to use modern 'docker compose' syntax

Development workflow:

• Start: docker compose -f compose.dev.yaml up --build
• Edit code and cargo-watch automatically recompiles
• No manual rebuilds or restarts needed

Fixes #313 - probably