FIX: Replace all text editors with unified CodeMirror interface

This commit enhances the user experience by standardizing all text editing
components to use CodeMirror, providing consistent functionality across the
entire application.

**Text Editor Unification**:
- Replaced all textarea elements with CodeMirror editors
- Unified syntax highlighting and line numbering across all text inputs
- Consistent oneDark theme implementation throughout the application

**Fixed Components**:
- FileViewer: Enhanced file editing with syntax highlighting for all file types
- CredentialEditor: Improved SSH key editing experience with code editor features
- HostManagerEditor: Better SSH private key input with proper formatting
- FileManagerGrid: Fixed new file/folder creation in empty directories

**Key Technical Improvements**:
- Fixed oneDark theme import path from @uiw/codemirror-themes to @codemirror/theme-one-dark
- Enhanced createIntent rendering logic to work properly in empty directories
- Added automatic createIntent cleanup when navigating between directories
- Configured consistent basicSetup options across all editors

**User Experience Enhancements**:
- Professional code editing interface for all text inputs
- Line numbers and syntax highlighting for better readability
- Consistent keyboard shortcuts and editing behavior
- Improved accessibility and user interaction patterns

Users now enjoy a unified, professional editing experience whether working with
code files, configuration files, or SSH credentials. The interface is consistent,
feature-rich, and optimized for developer workflows.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/ui/Desktop/Apps/File Manager/components/FileViewer.tsx

@@ -49,7 +49,7 @@ import {
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import CodeMirror from "@uiw/react-codemirror";
-import { oneDark } from "@uiw/codemirror-themes";
+import { oneDark } from "@codemirror/theme-one-dark";
 import { languages, loadLanguage } from "@uiw/codemirror-extensions-langs";
 
 interface FileItem {
@@ -802,13 +802,27 @@ export function FileViewer({
                         {renderHighlightedText(editedContent)}
                       </div>
                     ) : (
-                      // Directly show editable textarea
-                      <textarea
+                      // Use CodeMirror for all text files (unified editor experience)
+                      <CodeMirror
                         value={editedContent}
-                        onChange={(e) => handleContentChange(e.target.value)}
-                        className="w-full h-full p-4 border-none resize-none outline-none font-mono text-sm overflow-auto bg-background text-foreground"
+                        onChange={(value) => handleContentChange(value)}
+                        extensions={
+                          getLanguageExtension(file.name)
+                            ? [getLanguageExtension(file.name)!]
+                            : []
+                        }
+                        theme={oneDark}
+                        editable={isEditable}
                         placeholder={t("fileManager.startTyping")}
-                        spellCheck={false}
+                        className="h-full text-sm"
+                        basicSetup={{
+                          lineNumbers: true,
+                          foldGutter: true,
+                          dropCursor: false,
+                          allowMultipleSelections: false,
+                          highlightSelectionMatches: false,
+                          searchKeymap: true,
+                        }}
                       />
                     )}
                   </div>