feat(UninstallerType): detect Squirrel/Electron auto-updater installs (fixes half of #949)

[chirag127]

Summary

Adds detection for Squirrel / Electron auto-updater installers, a common class of modern Windows apps (Discord, GitHub Desktop, Slack classic, Teams classic, many Electron apps).

Their UninstallString is a stable pattern:

"C:\Users\<user>\AppData\Local\<Vendor>\<App>\Update.exe" --uninstall -s

Today BCU classifies these as Unknown (there's no matching branch in UninstallerTypeAdder.GetUninstallerType), which loses useful signal in the UI and blocks per-type filtering.

Changes

1. source/UninstallTools/UninstallerType.cs — add Squirrel enum value after PowerShell (+2 lines with the LocalisedName attribute).
2. source/UninstallTools/Factory/InfoAdders/UninstallerTypeAdder.cs — new detection branch, mirrors the existing PowerShell / Chocolatey shape (+7 lines).
3. source/UninstallTools/Properties/Localisation.resx — one string: UninstallerType_Squirrel → "Squirrel (Electron)" (+3 lines).
4. source/UninstallTools/Properties/Localisation.Designer.cs — matching accessor generated in the same style as UninstallerType_PowerShell (+9 lines).

Total: 23 lines added, 1 replaced across 4 files. No behavioural change for any existing uninstaller — Squirrel apps previously matched no branch and returned Unknown.

Detection logic

// Detect Squirrel / Electron auto-updater installs
// e.g. "C:\Users\<u>\AppData\Local\<Vendor>\<App>\Update.exe --uninstall -s"
// Discord, GitHub Desktop, Slack (classic), Teams (classic), many Electron apps
if (uninstallString.Contains("Update.exe", StringComparison.OrdinalIgnoreCase)
    && uninstallString.Contains("--uninstall", StringComparison.OrdinalIgnoreCase)
    && uninstallString.Contains(@"\AppData\Local\", StringComparison.OrdinalIgnoreCase))
    return UninstallerType.Squirrel;

The \AppData\Local\ clause avoids the (rare) case of a legit non-Squirrel Update.exe --uninstall living in Program Files or another install root.

Out of scope

• Junk scan integration. SpecificUninstallerKindScanner doesn't yet have a Squirrel case (%LocalAppData% leftovers, SquirrelTemp folders, stubexecutable shortcuts). Leaving as a follow-up so this PR stays surgical and reviewable.
• Package-manager delegation (e.g. asking winget to uninstall these when they were installed via winget install Discord.Discord) — see Prefer package-manager uninstall (winget / scoop / choco) over vendor uninstaller when app was installed via one #948, separate concern.

Related

Fixes half of #949 (detection half; junk-scan half left open there).

Test plan

• Build source/BulkCrapUninstaller.sln
• Scan a machine with Discord, GitHub Desktop, or Slack Classic installed
• Confirm the affected rows now show "Squirrel (Electron)" in the "Uninstaller type" column instead of "Unknown"
• Confirm all other rows are unchanged