chore(frontend): ignore src.main/ in prettier

src.main/ is an untracked generated artefact that was not covered by
the existing ignore patterns, causing pre-commit lint failures.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/.prettierignore

@@ -19,6 +19,7 @@ bun.lockb
 /src/lib/paraglide/
 /src/lib/paraglide_bak*/
 /src/paraglide/
+/src.main/
 /project.inlang/
 
 # Test artifacts