feat: use actual project data, real usage examples, dry-run/verbose flags, skip-unchanged optimization

- renderer: render_architecture_md accepts Config, uses project name and current date
- renderer: generate real Python usage examples from analyzed symbols
- writer: skip writing files when content unchanged (optimization)
- cli: add --dry-run flag to generate command (lists files without writing)
- cli: add verbose logging for file/module/symbol generation progress

archdoc-core/tests/full_pipeline.rs

@@ -142,7 +142,7 @@ fn test_renderer_produces_output() {
     let config = Config::default();
     let model = ProjectModel::new();
     let renderer = Renderer::new();
-    let result = renderer.render_architecture_md(&model);
+    let result = renderer.render_architecture_md(&model, None);
     assert!(result.is_ok(), "Renderer should produce output for empty model");
 }