Add loading splash screen for app startup

**Splash Screen Features:**
- Shows "Local Transcription" branding during startup
- Displays progress messages as app initializes
- Prevents users from clicking multiple times while loading
- Clean dark theme matching app design

**Implementation:**
- Created splash screen with custom pixmap drawing
- Updates messages during initialization phases:
  - "Loading configuration..."
  - "Creating user interface..."
  - "Starting web server..."
  - "Loading Whisper model..."
- Automatically closes when main window is ready
- Always stays on top to remain visible

**Benefits:**
- Better user experience during model loading (2-5 seconds)
- Prevents multiple app instances from confusion
- Professional appearance
- Clear feedback that app is starting

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

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

gui/main_window_qt.py

@@ -71,10 +71,13 @@ class ModelLoaderThread(QThread):
 class MainWindow(QMainWindow):
     """Main application window using PySide6."""
 
-    def __init__(self):
+    def __init__(self, splash_screen=None):
         """Initialize the main window."""
         super().__init__()
 
+        # Store splash screen reference
+        self.splash_screen = splash_screen
+
         # Application state
         self.is_transcribing = False
         self.config = Config()
@@ -101,14 +104,32 @@ class MainWindow(QMainWindow):
         self.setWindowTitle("Local Transcription")
         self.resize(900, 700)
 
+        # Update splash
+        self._update_splash("Creating user interface...")
+
         # Create UI
         self._create_widgets()
 
+        # Update splash
+        self._update_splash("Starting web server...")
+
+        # Start web server if enabled
+        self._start_web_server_if_enabled()
+
+        # Update splash
+        self._update_splash("Loading Whisper model...")
+
         # Initialize components (in background)
         self._initialize_components()
 
-        # Start web server if enabled
-        self._start_web_server_if_enabled()
+    def _update_splash(self, message: str):
+        """Update splash screen message if it exists."""
+        if self.splash_screen:
+            from PySide6.QtCore import Qt
+            from PySide6.QtGui import QColor
+            from PySide6.QtWidgets import QApplication
+            self.splash_screen.showMessage(message, Qt.AlignBottom | Qt.AlignCenter, QColor("#888888"))
+            QApplication.processEvents()
 
     def _create_widgets(self):
         """Create all UI widgets."""