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/src/components/layout/sidebar.tsx

@@ -24,6 +24,7 @@ import {
   Cpu,
   ChevronDown,
   Check,
+  BookOpen,
 } from "lucide-react";
 import {
   DropdownMenu,
@@ -68,6 +69,7 @@ export function Sidebar() {
       label: "Tools",
       items: [
         { id: "spec", label: "Spec Editor", icon: FileText },
+        { id: "context", label: "Context", icon: BookOpen },
         { id: "code", label: "Code View", icon: Code },
         { id: "analysis", label: "Analysis", icon: Search },
         { id: "tools", label: "Agent Tools", icon: Wrench },