Replace icon export workflow and add exact WinGet icon fallback

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• replace the old GitHub Actions and Python icon export flow with the local PowerShell exporter
• regenerate the icon database and add the workbook snapshot used as the checked-in source
• add a WinGet lookup fallback so icon resolution checks Winget., then the raw package id, then the normalized icon id

Details

• removes the obsolete update workflow and Python helper scripts
• adds scripts/update-icons.ps1 as the checked-in export and validation entry point
• refreshes WebBasedData/screenshot-database-v2.json, including the new Python.Launcher exact-match entry
• updates BasePkgDetailsHelper so WinGet packages can resolve exact package-id icons and screenshots before falling back to normalized ids

There were a few issues with the previous generation - trailing \n characters, but also trailing spaces. I noticed there are 114 package names truncated in the original excel file with "..." ellipsis, those will be fixed separately, as we need to recover the full package names.

For #4509 - I fixed the trailing \n character in the existing Python.Launcher entry, but the current UniGetUI code checks for "Winget.VendorName.PackageName" and then "PackageName", which is why it only looks for "Launcher". I updated the code to check for "Winget.VendorName.PackageName", then "VendorName.PackageName, and then "PackageName". Only 40 entries are prefixed with Winget currently, so I'll look into better ways to handle exact package id entries.