Read JSON (#1081)

Fixes #1037 
    
<!-- This is an auto-generated description by cubic. -->
---

## Summary by cubic
Enable JSON file support in codebase scanning so common configs and data
(e.g., package.json, vercel.json, translations) are included. Adds .json
to the allowed extensions and removes special-casing for
package.json/vercel.json.

<!-- End of auto-generated description by cubic. -->

e2e-tests/snapshots/context_manage.spec.ts_exclude-paths-precedence

@@ -46,7 +46,8 @@ You need to first add Supabase to your app and then we can add auth.
 ===
 role: user
 message: This is my codebase. <dyad-file path="manual/baz.json">
-// File contents excluded from context
+["even json is included"]
+
 </dyad-file>
 
 <dyad-file path="manual/file.ts">