docs: add logo and shields.io badges to README

- Add docs/nullrun-logo.png (NullRun NR logo) and render it centered
  at the top of README.md via raw.githubusercontent.com
- Add shields.io badges in two rows:
  * Release: PyPI version, Python versions, License, Downloads
  * Quality/Project: CI, Coverage, Stars, Documentation
- All badges use https:// (PyPI readme sanitizer strips http://)
- No classifier changes (left as-is per project decision)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: maltsev-dev

README.md

@@ -1,3 +1,38 @@
+<p align="center">
+  <img src="https://raw.githubusercontent.com/nullrunio/nullrun-sdk-python/master/docs/nullrun-logo.png"
+       alt="NullRun" width="320"/>
+</p>
+
+<p align="center">
+  <a href="https://pypi.org/project/nullrun/"><img
+    src="https://img.shields.io/pypi/v/nullrun?style=for-the-badge&logo=pypi&logoColor=white"
+    alt="PyPI version"/></a>
+  <a href="https://pypi.org/project/nullrun/#files"><img
+    src="https://img.shields.io/pypi/pyversions/nullrun?style=for-the-badge&logo=python&logoColor=white"
+    alt="Python versions"/></a>
+  <a href="https://github.com/nullrunio/nullrun-sdk-python/blob/master/LICENSE"><img
+    src="https://img.shields.io/pypi/l/nullrun?style=for-the-badge"
+    alt="License"/></a>
+  <a href="https://pypi.org/project/nullrun/"><img
+    src="https://img.shields.io/pypi/dm/nullrun?style=for-the-badge&color=blue"
+    alt="Downloads"/></a>
+</p>
+
+<p align="center">
+  <a href="https://github.com/nullrunio/nullrun-sdk-python/actions/workflows/ci.yml"><img
+    src="https://img.shields.io/github/actions/workflow/status/nullrunio/nullrun-sdk-python/ci.yml?style=for-the-badge&logo=github&label=CI"
+    alt="CI"/></a>
+  <a href="https://codecov.io/gh/nullrunio/nullrun-sdk-python"><img
+    src="https://img.shields.io/codecov/c/github/nullrunio/nullrun-sdk-python?style=for-the-badge&logo=codecov&logoColor=white"
+    alt="Coverage"/></a>
+  <a href="https://github.com/nullrunio/nullrun-sdk-python"><img
+    src="https://img.shields.io/github/stars/nullrunio/nullrun-sdk-python?style=for-the-badge&logo=github"
+    alt="Stars"/></a>
+  <a href="https://docs.nullrun.io"><img
+    src="https://img.shields.io/badge/docs-nullrun.io-0A66C2?style=for-the-badge&logo=readthedocs&logoColor=white"
+    alt="Documentation"/></a>
+</p>
+
 # nullrun
 
 **Enforcement gateway for AI agents.**