feat: Add web application interface

Implements a modern web-based interface alongside the existing desktop app.

Features:
- Flask backend with REST API and WebSocket support
- Responsive web UI with TailwindCSS and Alpine.js
- Real-time updates via Socket.IO
- All desktop features available in browser
- Multi-user support
- Mobile-friendly responsive design
- Same async import queue functionality

Technology Stack:
- Backend: Flask + Flask-SocketIO + Flask-CORS
- Frontend: HTML5 + TailwindCSS + Alpine.js
- Real-time: WebSocket (Socket.IO)
- Icons: Font Awesome 6

New Files:
- src/stocktool/web/app.py - Flask application server
- src/stocktool/web/templates/index.html - Main web interface
- src/stocktool/web/static/js/app.js - Alpine.js application logic
- WEB_APP.md - Complete web app documentation

API Endpoints:
- GET /api/config - Application configuration
- GET /api/locations - List locations
- POST /api/part/search - Search for part
- POST /api/part/import - Queue part import
- POST /api/stock/add - Add stock
- POST /api/stock/update - Update stock
- POST /api/stock/check - Check stock level
- POST /api/part/locate - Locate part
- GET /api/pending - Get pending imports

WebSocket Events:
- import_complete - Part import finished
- import_retry - Import failed, retrying
- import_failed - Import failed completely
- barcode_parsed - Barcode successfully parsed

Benefits:
- Access from any device with a browser
- No desktop installation required
- Better mobile experience
- Multiple users can work simultaneously
- Easier deployment and updates
- Network-accessible within local network

Usage:
  uv run stock-tool-web
  # Open browser to http://localhost:5000

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

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

README.md

@@ -2,6 +2,10 @@
 
 A comprehensive barcode scanning application for InvenTree inventory management.
 
+**Available in two versions:**
+- **Desktop App** (tkinter) - Traditional GUI application
+- **Web App** (Flask) - Modern browser-based interface **⭐ NEW!**
+
 ## Features
 
 - **Stock Addition**: Add stock to inventory by scanning barcodes
@@ -11,6 +15,7 @@ A comprehensive barcode scanning application for InvenTree inventory management.
 - **Async Part Import**: Non-blocking background import for unknown parts
 - **Server Connection Monitoring**: Real-time connection status
 - **Barcode Command Support**: Control the app via barcode commands
+- **Web Interface**: Access from any device with a browser (NEW!)
 
 ## Requirements
 
@@ -29,10 +34,16 @@ cd stocktool
 # Install with uv
 uv sync
 
-# Run the application
+# Run the DESKTOP application
 uv run stock-tool
+
+# OR run the WEB application
+uv run stock-tool-web
+# Then open browser to http://localhost:5000
 ```
 
+**👉 For Web App setup, see [WEB_APP.md](WEB_APP.md)**
+
 ### Manual Installation
 
 ```bash