docs(project): add reference Python/Flask implementation

Previous version of Tanabata used as visual and functional reference
for the new Go + SvelteKit rewrite.

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

docs/reference/backend/internal/storage/postgres/auth.go

@@ -0,0 +1,16 @@
+package postgres
+
+import "context"
+
+func UserLogin(ctx context.Context, name, password string) (user_id int, err error) {
+	row := connPool.QueryRow(ctx, "SELECT id FROM users WHERE name=$1 AND password=crypt($2, password)", name, password)
+	err = row.Scan(&user_id)
+	return
+}
+
+func UserAuth(ctx context.Context, user_id int) (ok, isAdmin bool) {
+	row := connPool.QueryRow(ctx, "SELECT is_admin FROM users WHERE id=$1", user_id)
+	err := row.Scan(&isAdmin)
+	ok = (err == nil)
+	return
+}