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/src/walkdir_discovery.rs

@@ -42,6 +42,27 @@ impl WalkdirDiscovery {
         }
     }
 
+    fn is_test_file(path: &Path, language: Language) -> 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 language {
+            Language::Rust => stem.ends_with("_test") || stem.ends_with("_tests"),
+            Language::Python => stem.starts_with("test_") || stem.ends_with("_test"),
+            Language::CSharp => stem.ends_with("Tests") || stem.ends_with("Test"),
+        }
+    }
+
     fn is_excluded(path: &Path, root: &Path, excludes: &[String]) -> bool {
         let relative = path.strip_prefix(root).unwrap_or(path);
         let relative_str = relative.to_string_lossy();
@@ -88,6 +109,18 @@ impl FileDiscovery for WalkdirDiscovery {
             }
 
             if let Some(language) = Self::detect_language(path) {
+                if !config.include_tests() && Self::is_test_file(path, language) {
+                    continue;
+                }
+                if let Some(changed) = config.changed_files() {
+                    let relative = path.strip_prefix(root).unwrap_or(path).to_string_lossy();
+                    if !changed
+                        .iter()
+                        .any(|c| relative.ends_with(c.as_str()) || c.ends_with(relative.as_ref()))
+                    {
+                        continue;
+                    }
+                }
                 let absolute = path.canonicalize().unwrap_or_else(|_| path.to_path_buf());
                 let file_path = FilePath::new(&absolute.to_string_lossy())
                     .map_err(|e| DomainError::IoError(e.to_string()))?;