feat(screensharing): list and share minimized windows on Windows

[vladopol]

On Windows, minimized (iconic) windows are missing from the "Choose what to share" picker: Chromium/WebRTC omits them from desktopCapturer.getSources() because a minimized window isn't rendered and can't produce frames (#1788). This especially hurts full-screen Remote Desktop windows, which have to be minimized to reach Talk — and then vanish from the picker.

This enumerates top-level windows natively and adds the minimized ones the capturer omits. On selection the window is restored so WebRTC can capture it, then sharing starts — the approach @ShGKme suggested in #1788 (enumerate via the Windows API, then activate the window like Zoom).

What it does

• Native enumeration via user32 (koffi FFI): EnumWindows with the standard Alt‑Tab filter (visible, unowned, not a tool window, has a title, not DWM‑cloaked).
• Minimized windows are added to Application windows with a Minimized badge and the window's own icon — read from the window via WM_GETICON (with a timeout so an unresponsive window can't block the picker) and converted from its HICON, matching the icon Windows shows in the taskbar and the one desktopCapturer provides for non‑minimized windows. No live preview — they have no frames until restored.
• On Share screen, the window is restored (ShowWindowAsync(SW_RESTORE) + SetForegroundWindow) before capture. Electron encodes the HWND in the window sourceId (window:<HWND>:0), so it stays valid after restoring.
• Windows‑only; no‑ops on macOS/Linux.

Dependency

Adds koffi (MIT, prebuilt — no node‑gyp/compilation). It is loaded lazily and only on Windows; kept out of the webpack bundle (external) and packaged for the target win32 arch only via a packageAfterCopy hook, with its .node unpacked from the asar archive. It is not shipped on macOS/Linux.

Testing

Verified on Windows 10 and 11 as a normal user: minimized windows (including Remote Desktop and non‑ASCII titles) are listed with the correct window icon, restore correctly on Share, and stream. Non‑minimized sharing is unchanged. ts:check and eslint pass.

Notes

• Capturing a window requires it to be un‑minimized; this restores it on selection, so the shared window briefly comes to the foreground (as Zoom does).
• When only a couple of windows are open, the dialog shows some empty space below the list — that is NcDialog's minimum content height, not specific to this change.

Closes #1788