Migrate backend from Lovable Cloud to own Supabase (EDU project)

- Point .env + supabase/config.toml at EDU (qgmcpounpkgsjlwosjdi)
- Replace Lovable Google-OAuth shim with native supabase.auth.signInWithOAuth
- Remove src/integrations/lovable and @lovable.dev/cloud-auth-js dependency
- Drop .lovable metadata; gitignore supabase/.temp

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -10,6 +10,10 @@ lerna-debug.log*
 node_modules
 dist
 dist-ssr
+
+# Supabase CLI local state
+supabase/.temp
+supabase/.branches
 .output
 .vinxi
 .tanstack/**