Add PCSC logo, default server settings, and Windows Sciter release helper

[tango103]

Motivation

• Add a visual brand mark to the desktop UI and ensure an inline helper for preparing Windows Sciter releases.
• Provide sensible defaults in the server settings dialog so new or empty configurations are prefilled.
• Remove the unused/hidden about settings tab from the settings tab list to reflect UI changes.

Description

• Adds flutter/assets/pcsc_logo.svg and renders it in desktop_home_page.dart using SvgPicture.asset with low opacity and IgnorePointer so it acts as a watermark.
• Imports package:flutter_svg/flutter_svg.dart in desktop_home_page.dart and adjusts logo sizing via isIncomingOnly check.
• Sets default values for server fields in showServerSettingsWithValue by adding defaultHost and defaultKey and initializing idCtrl, relayCtrl, and keyCtrl with those defaults when the existing values are empty.
• Removes SettingsTabKey.about from DesktopSettingPage.tabKeys and keeps the settings list conditional on build flags.
• Adds res/windows/README.md and res/windows/prepare_sciter_release.py, a helper script that inlines Sciter UI, builds rustdesk.exe with inline feature, and downloads the appropriate sciter.dll into a Release/ folder.

Testing

• No automated tests were executed as part of this change.

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Codex Task