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/mermaid/src/mermaid_renderer.rs

@@ -1,7 +1,7 @@
 use std::collections::{HashMap, HashSet};
 
 use archlens_domain::{
-    CodeElement, CodeGraph, DiagramLevel, DomainError, RelationshipKind, RenderOutput,
+    CodeElement, CodeGraph, DiagramLevel, DomainError, ModuleName, RelationshipKind, RenderOutput,
     RenderedFile, Visibility, ports::DiagramRenderer,
 };
 
@@ -46,20 +46,7 @@ impl MermaidRenderer {
     fn render_class_diagram(&self, graph: &CodeGraph) -> String {
         let mut lines = vec!["classDiagram".to_string()];
 
-        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();
         let has_namespaces = !grouped.is_empty();
 
         let mut seen: HashSet<String> = HashSet::new();
@@ -157,7 +144,7 @@ impl MermaidRenderer {
                 RelationshipKind::Import => {
                     let source_mod = file_to_module.get(rel.source());
                     let target_top = rel.target().split('.').next().unwrap_or("");
-                    let target_mod = Self::capitalize(target_top);
+                    let target_mod = ModuleName::capitalize(target_top);
 
                     if let Some(src) = source_mod
                         && modules.contains(&target_mod)
@@ -201,29 +188,10 @@ impl MermaidRenderer {
         lines.join("\n")
     }
 
-    fn capitalize(s: &str) -> String {
-        if s.is_empty() {
-            return String::new();
-        }
-        format!("{}{}", s[..1].to_uppercase(), &s[1..])
-    }
-
     fn render_project_flowchart(&self, graph: &CodeGraph) -> String {
         let mut lines = vec!["graph TD".to_string()];
 
-        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();
 
         for element in &ungrouped {
             let id = Self::sanitize_id(element.name());