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.

build/WebDropBridge.generated.wxs

@@ -0,0 +1,88 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi"
+     xmlns:ui="http://schemas.microsoft.com/wix/2010/ui"
+     xmlns:util="http://schemas.microsoft.com/wix/UtilExtension">
+    <Product Id="*" Name="Agravity Bridge" Language="1033" Version="0.8.4"
+        Manufacturer="agravity"
+        UpgradeCode="4a7c80da-6170-4d88-8efc-3f30636f6392">
+
+        <Package InstallerVersion="200" Compressed="yes" InstallScope="perMachine" Platform="x64" />
+        <Media Id="1" Cabinet="AgravityBridge.cab" EmbedCab="yes" />
+        
+        <!-- Required property for WixUI_InstallDir dialog set -->
+        <Property Id="WIXUI_INSTALLDIR" Value="INSTALLFOLDER" />
+        
+        <!-- Application Icon -->
+        <Icon Id="AppIcon.ico" SourceFile="C:\Development\VS Code Projects\webdrop_bridge\resources\icons\app.ico" />
+        
+        <!-- Custom branding for InstallDir dialog set -->
+        <WixVariable Id="WixUIDialogBmp" Value="C:\Development\VS Code Projects\webdrop_bridge\resources\icons\background.bmp" />
+        <WixVariable Id="WixUIBannerBmp" Value="C:\Development\VS Code Projects\webdrop_bridge\resources\icons\banner.bmp" />
+        <WixVariable Id="WixUILicenseRtf" Value="C:\Development\VS Code Projects\webdrop_bridge\resources\license.rtf" />
+
+        <!-- Installation UI dialogs -->
+        <UIRef Id="WixUI_InstallDir" />
+        <UIRef Id="WixUI_ErrorProgressText" />
+
+        <!-- Close running application before installation -->
+        <util:CloseApplication
+            Target="AgravityBridge.exe"
+            CloseMessage="yes"
+            RebootPrompt="no"
+            ElevatedCloseMessage="no" />
+
+        <Feature Id="ProductFeature" Title="Agravity Bridge" Level="1">
+            <ComponentGroupRef Id="AppFiles" />
+            <ComponentRef Id="ProgramMenuShortcut" />
+            <ComponentRef Id="DesktopShortcut" />
+        </Feature>
+
+        <Directory Id="TARGETDIR" Name="SourceDir">
+            <Directory Id="ProgramFiles64Folder">
+                <Directory Id="INSTALLFOLDER" Name="Agravity Bridge" />
+            </Directory>
+            <Directory Id="ProgramMenuFolder">
+                <Directory Id="ApplicationProgramsFolder" Name="Agravity Bridge"/>
+            </Directory>
+            <Directory Id="DesktopFolder" />
+        </Directory>
+
+        <DirectoryRef Id="ApplicationProgramsFolder">
+            <Component Id="ProgramMenuShortcut" Guid="*">
+                <Shortcut Id="ApplicationStartMenuShortcut"
+                    Name="Agravity Bridge"
+                    Description="Agravity drag-and-drop bridge"
+                    Target="[INSTALLFOLDER]AgravityBridge.exe"
+                    Icon="AppIcon.ico"
+                    IconIndex="0"
+                    WorkingDirectory="INSTALLFOLDER" />
+                <RemoveFolder Id="ApplicationProgramsFolderRemove"
+                    On="uninstall" />
+                <RegistryValue Root="HKCU"
+                    Key="Software\Microsoft\Windows\CurrentVersion\Uninstall\AgravityBridge"
+                    Name="installed"
+                    Type="integer"
+                    Value="1"
+                    KeyPath="yes" />
+            </Component>
+        </DirectoryRef>
+
+        <DirectoryRef Id="DesktopFolder">
+            <Component Id="DesktopShortcut" Guid="*">
+                <Shortcut Id="DesktopApplicationShortcut"
+                    Name="Agravity Bridge"
+                    Description="Agravity drag-and-drop bridge"
+                    Target="[INSTALLFOLDER]AgravityBridge.exe"
+                    Icon="AppIcon.ico"
+                    IconIndex="0"
+                    WorkingDirectory="INSTALLFOLDER" />
+                <RegistryValue Root="HKCU"
+                    Key="Software\AgravityBridge"
+                    Name="DesktopShortcut"
+                    Type="integer"
+                    Value="1"
+                    KeyPath="yes" />
+            </Component>
+        </DirectoryRef>
+    </Product>
+</Wix>