docs(readme): add codecov badge and star history chart

Adds the codecov badge to the badge row alongside the existing Tests
badge so the coverage signal sits next to the build signal. Adds a
Star History chart between Contributing and License using the
star-history.com embed, with light/dark variants via <picture>.

The codecov badge depends on the codecov integration being wired up
for agentrhq/authsome; if it isn't yet, the badge will render as
"unknown" until the integration is enabled.

Author: zriyansh

README.md

@@ -12,6 +12,7 @@
   <a href="https://opensource.org/licenses/MIT"><img src="https://img.shields.io/badge/License-MIT-yellow.svg" alt="License: MIT"></a>
   <a href="https://pypi.org/project/authsome/"><img src="https://img.shields.io/pypi/dm/authsome.svg" alt="PyPI downloads"></a>
   <a href="https://github.com/agentrhq/authsome/actions/workflows/test.yml"><img src="https://github.com/agentrhq/authsome/actions/workflows/test.yml/badge.svg" alt="Tests"></a>
+  <a href="https://codecov.io/gh/agentrhq/authsome"><img src="https://codecov.io/gh/agentrhq/authsome/branch/main/graph/badge.svg" alt="codecov"></a>
   <a href="https://discord.gg/9YP2C9tvMp"><img src="https://img.shields.io/badge/Discord-Join-5865F2?logo=discord&logoColor=white" alt="Discord"></a>
 </p>
 
@@ -175,6 +176,16 @@ See the [responsible disclosure policy](https://authsome.agentr.dev/docs/securit
 
 Contributions welcome. See [CONTRIBUTING.md](CONTRIBUTING.md) for development setup, testing, and the engineering principles we follow.
 
+## Star History
+
+<a href="https://star-history.com/#agentrhq/authsome&Date">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="https://api.star-history.com/svg?repos=agentrhq/authsome&type=Date&theme=dark">
+    <source media="(prefers-color-scheme: light)" srcset="https://api.star-history.com/svg?repos=agentrhq/authsome&type=Date">
+    <img alt="Star History Chart" src="https://api.star-history.com/svg?repos=agentrhq/authsome&type=Date">
+  </picture>
+</a>
+
 ## License
 
 MIT. See [LICENSE](LICENSE).