feat: Implement default welcome page for missing web application

- Added a professional HTML welcome page displayed when no web application is configured.
- Enhanced `_load_webapp()` method to support improved path resolution for both development and bundled modes.
- Updated error handling to show the welcome page instead of a bare error message when the webapp file is not found.
- Modified unit tests to verify the welcome page is displayed in error scenarios.

build: Complete Windows and macOS build scripts

- Created `build_windows.py` for building Windows executable and optional MSI installer using PyInstaller.
- Developed `build_macos.sh` for creating macOS application bundle and DMG image.
- Added logging and error handling to build scripts for better user feedback.

docs: Add build and icon requirements documentation

- Created `PHASE_3_BUILD_SUMMARY.md` detailing the build process, results, and next steps.
- Added `resources/icons/README.md` outlining icon requirements and creation guidelines.

chore: Sync remotes script for repository maintenance

- Introduced `sync_remotes.ps1` PowerShell script to fetch updates from origin and upstream remotes.

resources/icons/README.md

@@ -0,0 +1,47 @@
+# Icon Files for WebDrop Bridge
+
+This directory should contain application icon files for the build process.
+
+## Required Icons
+
+### Windows
+- **app.ico** - 256x256 or larger, ICO format
+  - Used by PyInstaller and Windows installer
+  - Can contain multiple resolutions (16, 32, 48, 64, 128, 256)
+
+### macOS
+- **app.icns** - Apple icon set
+  - Required for macOS .app bundle
+  - Must include at least: 16, 32, 48, 64, 128, 256, 512, 1024px sizes
+  - Tools: `iconutil` on macOS, or `png2icns`
+
+## Creating Icons
+
+### From PNG on macOS:
+```bash
+png2icns resources/icons/app.icns resources/icons/app-1024.png
+```
+
+### From Multiple PNGs on macOS:
+```bash
+mkdir app.iconset
+# Add PNG files: 16x16, 32x32, 64x64, 128x128, 256x256, 512x512, 1024x1024
+iconutil -c icns app.iconset -o resources/icons/app.icns
+```
+
+### Creating ICO from PNG on Windows:
+- Use tools like: ImageMagick, GIMP, or online converters
+- Ensure high quality for professional appearance
+
+## Current Status
+
+⚠️ Icon files are currently missing.
+- The build scripts will work without them (PyInstaller uses default icon)
+- Replace these files before distribution for professional appearance
+
+## Design Guidelines
+
+- Use consistent branding/color scheme
+- Ensure visibility at small sizes (16x16)
+- Include transparency for professional look
+- Test on both light and dark backgrounds (macOS)