fix: add .html extensions to documentation links in README

Fixes broken documentation links that were pointing to directory-style URLs
without .html extensions. The MkDocs site requires .html extensions for
all documentation pages.

Updated links:
- Getting Started Guide
- Wrappers Guide
- Adapters Guide
- API Reference (both locations)

Fixes #182

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
Co-Authored-By: William Easton <[email protected]>

Author: 3 people

README.md

@@ -9,10 +9,10 @@ This monorepo contains two libraries:
 ## Documentation
 
 - [Full Documentation](https://strawgate.com/py-key-value/)
-- [Getting Started Guide](https://strawgate.com/py-key-value/getting-started/)
-- [Wrappers Guide](https://strawgate.com/py-key-value/wrappers/)
-- [Adapters Guide](https://strawgate.com/py-key-value/adapters/)
-- [API Reference](https://strawgate.com/py-key-value/api/protocols/)
+- [Getting Started Guide](https://strawgate.com/py-key-value/getting-started.html)
+- [Wrappers Guide](https://strawgate.com/py-key-value/wrappers.html)
+- [Adapters Guide](https://strawgate.com/py-key-value/adapters.html)
+- [API Reference](https://strawgate.com/py-key-value/api/protocols.html)
 
 ## Why use this library?
 
@@ -354,7 +354,7 @@ library.
 ## Project links
 
 - [Full Documentation](https://strawgate.com/py-key-value/)
-- [API Reference](https://strawgate.com/py-key-value/api/protocols/)
+- [API Reference](https://strawgate.com/py-key-value/api/protocols.html)
 
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