Update Dockerfile for multi-architecture support and enhance coding rules

- Modify Dockerfile to support multi-platform builds using TARGETARCH.
- Update coderule.mdc to enforce source code organization under the `src/` directory.
- Remove outdated rule from python.mdc regarding `src/` layout.

.cursor/rules/coderule.mdc

@@ -21,3 +21,4 @@ alwaysApply: true
 
 - Make sure we don't commit binaries, create and keep .gitignore up to date and delete binaries after you are done with the task
 - Never force-push to main or dev branches
+- Place all source code under the `src/` directory; keep project-level config, tests, and tooling at the repo root

.cursor/rules/python.mdc

@@ -8,7 +8,6 @@ globs: ["**/*.py", "**/pyproject.toml", "**/requirements*.txt"]
 - Use type hints on all function signatures; validate with `mypy` or `pyright`
 - Use `pydantic` for data validation and serialization
 - Import order: stdlib -> third-party -> local; use absolute imports
-- Use `src/` layout to separate app code from project files
 - Use context managers (`with`) for resource management
 - Catch specific exceptions, never bare `except:`; use custom exception classes
 - Use `async`/`await` with `asyncio` for I/O-bound concurrency