refactor: move scattered business logic into domain

- CodeGraph::merge_project_edges() replaces presentation-layer function
- Language::is_test_file() centralises test file detection (was in walkdir)
- AnalysisConfig::is_standard_excluded() centralises default dir exclusions (was in walkdir)
- normalize_cargo_package() / normalize_python_package() in domain replace duplicated normalisers in each adapter
- walkdir, cargo-workspace, python-project updated to call domain methods

crates/domain/src/value_objects/source/language.rs

@@ -1,3 +1,5 @@
+use std::path::Path;
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Language {
     Rust,
@@ -13,4 +15,26 @@ impl Language {
             Self::Python => "Python",
         }
     }
+
+    pub fn is_test_file(&self, path: &Path) -> bool {
+        let stem = path
+            .file_stem()
+            .and_then(|s| s.to_str())
+            .unwrap_or_default();
+
+        let in_tests_dir = path
+            .parent()
+            .map(|p| p.components().any(|c| c.as_os_str() == "tests"))
+            .unwrap_or(false);
+
+        if in_tests_dir {
+            return true;
+        }
+
+        match self {
+            Self::Rust => stem.ends_with("_test") || stem.ends_with("_tests"),
+            Self::Python => stem.starts_with("test_") || stem.ends_with("_test"),
+            Self::CSharp => stem.ends_with("Tests") || stem.ends_with("Test"),
+        }
+    }
 }

crates/domain/src/value_objects/source/mod.rs

@@ -7,3 +7,11 @@ pub use file_path::FilePath;
 pub use language::Language;
 pub use module_name::ModuleName;
 pub use source_file::SourceFile;
+
+pub fn normalize_cargo_package(name: &str) -> String {
+    name.replace('_', "-")
+}
+
+pub fn normalize_python_package(name: &str) -> String {
+    name.to_lowercase().replace(['-', '.'], "_")
+}