feat(diagnostics): make diagnostic messages selectable and copyable

- Refactor diagnostic rendering to use DOM elements (`span.diagnostic`) instead of CSS `::after` pseudo-elements
- Add `DiagnosticRenderer` to manage diagnostic message lifecycle
- Update `Selection` and `Mouse` logic to ignore diagnostic elements during code navigation and cursor placement
- Implement `isInsideDiagnostic` and `getLineTextLength` helpers to correctly handle mixed content lines
- Allow native text selection and copying for diagnostics by bypassing default editor events when interacting with them
- Prevent diagnostic selection interference when selecting code via `.code.selecting` CSS state
- Update backend ignore defaults to include `target` and `node_modules`

Author: vipmax

anycode-backend/src/utils.rs

@@ -7,6 +7,8 @@ pub const DEFAULT_IGNORE_DIRS: &[&str] = &[
     ".git",
     // Python
     "__pycache__", ".pytest_cache", 
+    
+    "target", "node_modules",
 ];
 
 pub const DEFAULT_IGNORE_FILES: &[&str] = &[

anycode-base/src/cursor.ts

@@ -1,4 +1,4 @@
-import { AnycodeLine } from './utils';
+import { AnycodeLine, isDiagnosticElement } from './utils';
 
 export function removeCursor() {
     const sel = window.getSelection();
@@ -18,7 +18,10 @@ export function moveCursor(
 
     var character: number = column;
 
-    const chunks = Array.from(lineDiv.children).map(l => l as AnycodeLine);
+    const chunks = Array.from(lineDiv.children)
+        .filter((child) => !isDiagnosticElement(child))
+        .map(l => l as AnycodeLine);
+        
     let chunkCharacter = 0;
     let chunk: Element | null = null;