Add brand-specific update channel and environment configuration

- Updated `brand_config.py` to include `WEBDROP_UPDATE_CHANNEL` in the environment variables.
- Enhanced `build_macos.sh` to create a bundled `.env` file with brand-specific defaults, including the update channel.
- Implemented a method in `build_windows.py` to create a bundled `.env` file for Windows builds, incorporating brand-specific runtime defaults.
- Modified `config.py` to ensure the application can locate the `.env` file in various installation scenarios.
- Added unit tests in `test_config.py` to verify the loading of the bootstrap `.env` from the PyInstaller runtime directory.
- Generated new WiX object and script files for the Windows installer, including application shortcuts and registry entries.

src/webdrop_bridge/config.py

@@ -408,7 +408,15 @@ class Config:
             candidate_paths.append(Path(env_file).resolve())
         else:
             if getattr(sys, "frozen", False):
-                candidate_paths.append(Path(sys.executable).resolve().parent / ".env")
+                exe_dir = Path(sys.executable).resolve().parent
+                # One-folder fallback: some packagers place data files in _internal.
+                candidate_paths.append(exe_dir / ".env")
+                candidate_paths.append(exe_dir / "_internal" / ".env")
+
+                # PyInstaller runtime extraction directory (one-file and one-folder).
+                meipass = getattr(sys, "_MEIPASS", None)
+                if meipass:
+                    candidate_paths.append(Path(meipass).resolve() / ".env")
 
             candidate_paths.append(Path.cwd() / ".env")
             candidate_paths.append(Path(__file__).resolve().parents[2] / ".env")