feat: add rendering-primitives crate, share non_import_rels across renderers

crates/adapters/mermaid/src/mermaid_renderer.rs

@@ -4,6 +4,7 @@ use archlens_domain::{
     CodeElement, CodeGraph, DiagramLevel, DomainError, ModuleName, RelationshipKind, RenderOutput,
     RenderedFile, Visibility, ports::DiagramRenderer,
 };
+use archlens_rendering_primitives::non_import_rels;
 
 pub struct MermaidRenderer {
     level: DiagramLevel,
@@ -94,14 +95,11 @@ impl MermaidRenderer {
         lines.extend(deferred_members);
 
         let mut rel_seen: HashSet<String> = HashSet::new();
-        for rel in graph.relationships() {
-            if rel.kind() == RelationshipKind::Import {
-                continue;
-            }
+        for rel in non_import_rels(graph.relationships()) {
             let arrow = match rel.kind() {
                 RelationshipKind::Inheritance => "<|--",
                 RelationshipKind::Composition => "-->",
-                RelationshipKind::Import => "..>",
+                RelationshipKind::Import => unreachable!("imports filtered by non_import_rels"),
             };
             let src = Self::display_name(rel.source());
             let tgt = Self::display_name(rel.target());