refactor: deepen modules, consolidate inference, delete dead code

- Extract build_graph/load_config/create_renderer in presentation (393→~250 lines)
- Move module inference into ModuleName::from_path(), delete 3 scattered copies
- Move resolve_relationships/filter_external_imports into CodeGraph
- Add LanguageExtractor trait in tree-sitter adapter
- Add CodeGraph::elements_by_module(), replace 6 identical grouping loops
- Delete dead RenderDiagrams query

crates/adapters/ascii/src/ascii_renderer.rs

@@ -1,5 +1,3 @@
-use std::collections::HashMap;
-
 use archlens_domain::{
     CodeElement, CodeGraph, DomainError, RelationshipKind, RenderOutput, RenderedFile,
     ports::DiagramRenderer,
@@ -55,19 +53,7 @@ impl DiagramRenderer for AsciiRenderer {
             return Ok(RenderOutput::single(file));
         }
 
-        let mut grouped: HashMap<String, Vec<&CodeElement>> = HashMap::new();
-        let mut ungrouped: Vec<&CodeElement> = Vec::new();
-
-        for element in graph.elements() {
-            if let Some(module) = element.module() {
-                grouped
-                    .entry(module.as_str().to_string())
-                    .or_default()
-                    .push(element);
-            } else {
-                ungrouped.push(element);
-            }
-        }
+        let (grouped, ungrouped) = graph.elements_by_module();
 
         if !ungrouped.is_empty() {
             lines.push(String::new());