feat: prepare mi-fitness-mcp for first public release

Package the standalone Mi Fitness MCP with clearer public docs, release metadata, CI, and safer local repository hygiene so it is ready to publish without secrets or work identity leakage.

CONTRIBUTING.md

@@ -0,0 +1,25 @@
+# Contributing
+
+Thanks for contributing.
+
+## Local setup
+
+```bash
+python -m venv .venv
+source .venv/bin/activate
+pip install -e '.[dev]'
+```
+
+## Before opening a change
+
+- keep local config, SQLite data, and captured cloud payloads out of git
+- never commit real `userId` or `passToken` values
+- keep README and examples aligned with actual supported data types
+
+## Checks
+
+```bash
+ruff check src tests
+pytest
+python -m build
+```