scaffold laravel 12 backend

composer create-project laravel/laravel + artisan install:api.
sanctum removed (custom session-cookie auth per ai/backend-context).
personal_access_tokens migration + config/sanctum.php deleted.
default .gitignore excludes vendor/, .env, etc - composer install
recreates vendor at setup time.

backend/.gitattributes

@@ -0,0 +1,11 @@
+* text=auto eol=lf
+
+*.blade.php diff=html
+*.css diff=css
+*.html diff=html
+*.md diff=markdown
+*.php diff=php
+
+/.github export-ignore
+CHANGELOG.md export-ignore
+.styleci.yml export-ignore