feat: implement DCOS source tree, tests, and build configuration

Complete implementation of the DCOS package including:
- 40+ Python source files across agents, communication, core, learning, memory, protocols, utils
- pyproject.toml build configuration
- 102 unit tests across all subsystems
- Fixed flake.nix (Python 3.12, proper dependencies, pyproject build)
- Fixed .woodpecker.yml (correct paths, removed silent-fail flags)
- Added .gitignore
- Cleared stale pytest cache

src/dcos/__main__.py

@@ -0,0 +1,9 @@
+"""
+DCOS entry point — invoked via `python -m dcos`.
+"""
+
+import sys
+from .utils.cli import main
+
+if __name__ == "__main__":
+    sys.exit(main())