Add application icon support for GUI and compiled executables

Added platform-specific icon support for both the running application
and compiled executables:

New files:
- create_icons.py: Script to convert PNG to platform-specific formats
  - Generates .ico for Windows (16, 32, 48, 256px sizes)
  - Generates .iconset for macOS (ready for iconutil conversion)
- LocalTranscription.png: Source icon image
- LocalTranscription.ico: Windows icon file (multi-size)
- LocalTranscription.iconset/: macOS icon set (needs iconutil on macOS)

GUI changes:
- main.py: Set application-wide icon for taskbar/dock
- main_window_qt.py: Set window icon for GUI window

Build configuration:
- local-transcription.spec: Use platform-specific icons in PyInstaller
  - Windows builds use LocalTranscription.ico
  - macOS builds use LocalTranscription.icns (when generated)

To generate macOS .icns file on macOS:
  iconutil -c icns LocalTranscription.iconset

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

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

local-transcription.spec

@@ -157,7 +157,7 @@ exe = EXE(
     target_arch=None,
     codesign_identity=None,
     entitlements_file=None,
-    icon=None,  # Add icon file path here if you have one
+    icon='LocalTranscription.ico' if is_windows else 'LocalTranscription.icns',  # Platform-specific icon
 )
 
 coll = COLLECT(