Move Win32 show/hide/minimize/restore tray-chrome logic (the four user32 P/Invokes, the SW_* constants, and the _isMainWindowHidden flag) into Services/WindowChromeManager, and the DPI-aware bounds save/restore + Maximize logic into Services/WindowPlacementService. MainWindow's MainWindow_Closed now delegates to _placementService.Save(); HideShowMainWindow / MinimizeOrHideMainWindow / HideMainWindowToTray delegate to _chromeManager.
Also removes stale PlotBounds/PlotAxisLayout/PlotSeriesSample records that were left behind from the PlotView extraction (dead code; the records now live as private nested types in PlotView).
MainWindow shrinks from 1445 to 1362 lines; no behaviour change.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
JMR-devandCopilot
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