Implement context files feature - verified

- Added Context view with file list sidebar and text/image editor
- Added Context navigation item to sidebar
- Added deleteFile API method to Electron IPC
- Updated coding_prompt.md to include Step 1.5 for loading context files
- Updated mock Electron API to properly handle context directory
- Added test utilities for context view navigation

Features:
- Left panel with list of all context files
- Text editor for editing .md, .txt, and other text files
- Image preview for .png, .jpg, .gif, and other image files
- Add new text or image files via dialog
- Delete files with confirmation dialog
- Drag and drop file upload support
- Auto-save detection with Save button

All Playwright tests passing (9/9)
Deleted test file after verification

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/electron/main.js

@@ -146,6 +146,15 @@ ipcMain.handle("fs:stat", async (_, filePath) => {
   }
 });
 
+ipcMain.handle("fs:deleteFile", async (_, filePath) => {
+  try {
+    await fs.unlink(filePath);
+    return { success: true };
+  } catch (error) {
+    return { success: false, error: error.message };
+  }
+});
+
 // App data path
 ipcMain.handle("app:getPath", (_, name) => {
   return app.getPath(name);