Enhance Windows installer configuration and add license file

- Updated the WiX configuration in build_windows.py to include required properties for the WixUI_InstallDir dialog.
- Changed the UI reference from WixUI_Minimal to WixUI_InstallDir for improved installation experience.
- Added custom branding images for the installer UI using WixVariable for background and banner images.
- Introduced a new license.rtf file containing the MIT License for the WebDrop Bridge project.
- Updated binary resources for background and banner images.

resources/license.rtf

@@ -0,0 +1,18 @@
+{\rtf1\ansi\ansicpg1252\cocoartf2\cuc
+{\fonttbl\f0\fswiss Helvetica;}
+{\colortbl;\red255\green255\blue255;}
+{\*\expandedcolortbl;;}
+\margl1440\margr1440\vieww11900\viewh8605\viewkind0
+\pard\tx720\tx1440\tx2160\tx2880\tx3600\tx4320\tx5040\tx5760\tx6480\tx7200\tx7920\tx8640\pardirnatural\partightenfocus1
+
+\f0\fs20 \cf0 WebDrop Bridge - License Agreement\
+\
+\b MIT License\b0\
+\
+Copyright (c) 2026 HIM-Tools\
+\
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:\
+\
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.\
+\
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.}