feat: implement all P1/P2/P3/P4 improvements from issue backlog

P1 correctness:
- filter test files by default (--include-tests to opt in)
- per-module diagrams show cross-module dependency arrows
- qualified type names (Module::TypeName) fix false edges from duplicate names

P2 output richness:
- method parameter types and return types in class diagrams (Rust + Python)
- Python pyproject.toml project analyzer (--level project for monorepos)

P3 unique value:
- boundary rules in archlens.toml ([rules] allow/deny, --strict enforcement)

P4 nice to have:
- dependency weight labels on module arrows (--no-weights to disable)
- --watch mode with 500ms debounce
- D2 renderer adapter (--format d2)
- interactive self-contained HTML viewer (--format html)
- git-aware incremental analysis (--since <ref>)

crates/adapters/walkdir/tests/walkdir_discovery_tests.rs

@@ -58,6 +58,100 @@ fn respects_exclude_patterns() {
     assert!(!files.iter().any(|f| f.path().as_str().contains("billing")));
 }
 
+#[test]
+fn excludes_python_test_prefix_files_by_default() {
+    let dir = tempfile::tempdir().unwrap();
+    fs::write(dir.path().join("orders.py"), "class Order: pass").unwrap();
+    fs::write(dir.path().join("test_orders.py"), "class TestOrder: pass").unwrap();
+
+    let discovery = WalkdirDiscovery::new();
+    let files = discovery
+        .discover(dir.path(), &AnalysisConfig::default())
+        .unwrap();
+
+    assert_eq!(files.len(), 1);
+    assert!(files[0].path().as_str().ends_with("orders.py"));
+}
+
+#[test]
+fn excludes_python_test_suffix_files_by_default() {
+    let dir = tempfile::tempdir().unwrap();
+    fs::write(dir.path().join("orders.py"), "class Order: pass").unwrap();
+    fs::write(dir.path().join("orders_test.py"), "class OrderTest: pass").unwrap();
+
+    let discovery = WalkdirDiscovery::new();
+    let files = discovery
+        .discover(dir.path(), &AnalysisConfig::default())
+        .unwrap();
+
+    assert_eq!(files.len(), 1);
+    assert!(files[0].path().as_str().ends_with("orders.py"));
+}
+
+#[test]
+fn excludes_files_in_tests_directory_by_default() {
+    let dir = tempfile::tempdir().unwrap();
+    fs::create_dir_all(dir.path().join("tests")).unwrap();
+    fs::write(dir.path().join("orders.py"), "class Order: pass").unwrap();
+    fs::write(dir.path().join("tests/helpers.py"), "class Helper: pass").unwrap();
+
+    let discovery = WalkdirDiscovery::new();
+    let files = discovery
+        .discover(dir.path(), &AnalysisConfig::default())
+        .unwrap();
+
+    assert_eq!(files.len(), 1);
+    assert!(files[0].path().as_str().ends_with("orders.py"));
+}
+
+#[test]
+fn excludes_rust_test_files_by_default() {
+    let dir = tempfile::tempdir().unwrap();
+    fs::write(dir.path().join("orders.rs"), "struct Order;").unwrap();
+    fs::write(dir.path().join("orders_tests.rs"), "struct OrdersTests;").unwrap();
+
+    let discovery = WalkdirDiscovery::new();
+    let files = discovery
+        .discover(dir.path(), &AnalysisConfig::default())
+        .unwrap();
+
+    assert_eq!(files.len(), 1);
+    assert!(files[0].path().as_str().ends_with("orders.rs"));
+}
+
+#[test]
+fn excludes_rust_files_in_tests_directory_by_default() {
+    let dir = tempfile::tempdir().unwrap();
+    fs::create_dir_all(dir.path().join("tests")).unwrap();
+    fs::write(dir.path().join("lib.rs"), "struct Lib;").unwrap();
+    fs::write(
+        dir.path().join("tests/integration.rs"),
+        "struct IntegrationTest;",
+    )
+    .unwrap();
+
+    let discovery = WalkdirDiscovery::new();
+    let files = discovery
+        .discover(dir.path(), &AnalysisConfig::default())
+        .unwrap();
+
+    assert_eq!(files.len(), 1);
+    assert!(files[0].path().as_str().ends_with("lib.rs"));
+}
+
+#[test]
+fn include_tests_flag_re_enables_test_files() {
+    let dir = tempfile::tempdir().unwrap();
+    fs::write(dir.path().join("orders.py"), "class Order: pass").unwrap();
+    fs::write(dir.path().join("test_orders.py"), "class TestOrder: pass").unwrap();
+
+    let config = AnalysisConfig::default().with_include_tests(true);
+    let discovery = WalkdirDiscovery::new();
+    let files = discovery.discover(dir.path(), &config).unwrap();
+
+    assert_eq!(files.len(), 2);
+}
+
 #[test]
 fn empty_directory_returns_no_files() {
     let dir = tempfile::tempdir().unwrap();