Add application icon for all platforms

- Created icon generation script (create_icon.py)
- Generated PNG icon (512x512) with word search grid design
- Generated ICO file for Windows (multi-resolution)
- Updated PyInstaller spec to use platform-appropriate icons
- Updated .gitignore to exclude generated icon size variants

Icon features:
- Light blue gradient background
- 5x5 grid with letters spelling WORD, SEARCH, etc.
- Highlighted "WORD" in green to show found word
- Professional, clean design

Windows: icon.ico
macOS: icon.icns (generate on macOS with provided commands)
Linux: icon.png

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

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

.gitignore

@@ -42,3 +42,9 @@ Thumbs.db
 
 # Generated PDF files (optional - uncomment if you don't want to track PDFs)
 # *.pdf
+
+# Generated icon files (sizes)
+icon_*.png
+
+# macOS icon set directory
+icon.iconset/