fix(lint): exclude project.inlang/ from Prettier

Inlang regenerates .meta.json and README.md on every compilation run.
The regenerated files fail Prettier in CI because the tool writes its
own formatting, not ours.

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

frontend/.prettierignore

@@ -18,6 +18,7 @@ bun.lockb
 /src/lib/paraglide/
 /src/lib/paraglide_bak*/
 /src/paraglide/
+/project.inlang/
 
 # Test artifacts
 /test-results/