Update Discord link in 'When to Write a SEP' to community page

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dend

docs/community/sep-guidelines.mdx

@@ -31,7 +31,7 @@ The SEP process is reserved for changes that are substantial enough to require b
 - Adding examples to existing features
 - Minor schema fixes that don't change behavior
 
-Not sure? Ask in [Discord](https://discord.gg/6CSzBmMkjX) before starting significant work.
+Not sure? Ask in [Discord](/community/communication#discord) before starting significant work.
 
 ## SEP Types