Fix: Properties window, theme backgrounds, rename, sidebar toggle and icon

[MemerGamer]

Fixes found on a real KDE Wayland (dark) desktop.

• Backgrounds: the startup resource loader overwrote App.Theme.BackgroundBrush with Transparent (a Windows Mica placeholder), leaving tab strip, sidebar and Properties black. On Linux the solid theme fill from LinuxDesktopResources is kept (dark and light).
• Properties: applies the resolved app theme like the main window, no Mica backdrop, and is really closed on Linux (the hidden cached window stayed mapped as a black rectangle, so Cancel/Close looked dead).
• Inline rename: List and Grid layouts never showed the box (FindName does not resolve template names under Uno, and x:Load deferral); now found via the visual tree. Rename box gets explicit theme colours. Slow second click renames after the normal delay; a fast double click opens the item (verified).
• Hamburger: VM mode changed but the control kept a local DisplayMode set by the adaptive visual state; the button now toggles compact/expanded (flyout in minimal mode) and the control mirrors the VM mode.
• About: upstream sponsor card hidden on Linux unless Constants.ExternalUrl.ForkSupportUrl is set (also the sponsor prompt).
• Icons: rebuilt every size from the trimmed 600px tile with Lanczos plus a vector penguin badge (packaging/linux/icons/penguin-badge*.svg) rasterised at final size.

Known: Grid layout rendering at some sizes is blurry in headless (unrelated), and a row renamed in Details can keep light-on-light text after switching layout in light theme.

🤖 Generated with Claude Code

https://claude.ai/code/session_01LeKXJc3DnK3PzAqwgA72NY