Remove unused dependencies and dead code, refresh AGENTS.md

- Drop unused email module and media text extraction path
- Remove 12 unused dependencies
- Remove unused imports in server.ts
- Add typecheck and test scripts
- Rewrite AGENTS.md to describe this project

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/pages/api/admin/upload-media.ts

@@ -41,7 +41,6 @@ export const handler: BunextAPIRouteHandler<APIResponseObject> = async (
             is_media_primary,
             update_on_duplicate,
             reauth,
-            return_media_text_content,
             media,
             is_media_private,
             media_name,
@@ -61,7 +60,6 @@ export const handler: BunextAPIRouteHandler<APIResponseObject> = async (
             media_type,
             is_primary: is_media_primary,
             update_on_duplicate,
-            extract_media_text_content: return_media_text_content,
             media,
             media_mime_type: ext,
             user: { id: twuiNumberfy(user_id) },