fix: KF6Attica recipe, kf6-knewstuff Attica dep, topo-sort cycle error

- Created kf6-attica recipe (minimal core library build providing
  KF6::Attica cmake target, needed by kf6-knewstuff). v6.10.0,
  QML/tests/examples disabled.
- Added kf6-attica to redbear-full.toml config, integrate-redbear.sh
  symlink, and recipes/kde/ symlink.
- Fixed kf6-knewstuff: removed stale find_package(KF6Attica)
  suppression; added kf6-attica as dependency. Now publishes
  to repo (core-only build produces empty package — upstream
  code structure yields no libs with QtQuick/widgets/tools off).
- Cookbook topo-sort: changed cycle fallback from silent
  Ok(recipes) to Err(Recursion) — surfaces dependency graph
  bugs instead of hiding them.
- Fixed stale QtNetwork comment: QtNetwork IS enabled in qtbase
  since 2026-04-29 (relibc DNS resolver hardened).
- Verified: kf6-attica builds, kf6-knewstuff publishes to repo

src/recipe.rs

@@ -570,7 +570,7 @@ fn topological_sort(recipes: Vec<CookRecipe>) -> Result<Vec<CookRecipe>, Package
     }
 
     if sorted.len() != recipes.len() {
-        return Ok(recipes);
+        return Err(PackageError::Recursion(Default::default()));
     }
 
     Ok(sorted)