[CrossChEp]

Fullscreen media previews disappear when Telegram loses focus,
preventing users from keeping an image visible on one display
while working in another application on a second display.

Keep the viewer visible at the normal window level while Telegram
is inactive, allowing other applications to cover it. Restore the
overlay level when Telegram becomes active again.

Validation:

• Debug build on macOS 27, Apple Silicon.
• Manually verified the two-display image-viewing scenario.

Before:

before-under-10mb.mp4

After:

after-under-10mb.mp4

[ilya-fedin]

Why this change?

[CLAassistant]

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