Add Context7 claim file (#21110)

Adds context7.json to claim this repository for Context7 documentation service.

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

Co-authored-by: Phil Whittaker <[email protected]>
Co-authored-by: Claude <[email protected]>

Author: 3 people

context7.json

@@ -0,0 +1,4 @@
+{
+  "url": "https://context7.com/umbraco/umbraco-cms",
+  "public_key": "pk_GTIgsrGAQiHNxCirZBDIM"
+}