feat(desktop): Linux AppImage polish — window controls, updater UX, docs (#2144)

* feat(electron): add Linux AppImage releases

* ci: cache Linux OpenCode CLI artifacts

* fix(ci): await Linux release inventory check

* fix(electron): add frameless window controls on Linux desktop

Linux AppImages were created without native WM decorations and without
in-app controls, leaving users unable to close the window with a mouse.

Treat Linux like Windows: frameless BrowserWindow plus the existing
WindowsWindowControls header buttons and app-menu entry. macOS keeps
hidden title bar with traffic lights unchanged.

Shared usesFramelessElectronChrome() helper drives main window, mini
chat, header insets, and titlebar controls.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* feat(desktop): add configurable window controls position by OS

Add desktopWindowControlsPosition setting (auto/left/right) with OS-aware
defaults: Linux left, Windows right. Wire frameless chrome controls in
Header, TitlebarLeftControls, and MiniChatLayout, plus a Sessions settings
control for Windows and Linux desktop shells.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(desktop): address Linux AppImage release review findings

Propagate updater capability errors to the UI, treat missing
latest-linux.yml feeds as no-update, stop installed-apps IPC spam on
Linux, document FUSE/AppImage limits, add CHANGELOG entry, migrate
remaining btriapitsyn URLs, and run Electron Linux unit tests on PRs.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: jibanez-staticduo <staticduo@gmail.com>
Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/components/layout/TitlebarLeftControls.tsx

@@ -6,8 +6,10 @@ import { useUIStore } from '@/stores/useUIStore';
 import { useI18n } from '@/lib/i18n';
 import { useProjectActionsContext } from '@/hooks/useProjectActionsContext';
 import { ProjectActionsButton } from '@/components/layout/ProjectActionsButton';
+import { WindowsWindowControls } from '@/components/desktop/WindowsWindowControls';
 import { formatShortcutForDisplay, getEffectiveShortcutCombo } from '@/lib/shortcuts';
 import { invokeDesktop } from '@/lib/desktop';
+import { useDesktopWindowControlsLayout } from '@/hooks/useDesktopWindowControlsLayout';
 
 const ICON_BUTTON_CLASS =
   'app-region-no-drag inline-flex h-8 w-8 items-center justify-center gap-2 rounded-md typography-ui-label font-medium text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary hover:bg-interactive-hover transition-colors';
@@ -32,12 +34,7 @@ export const TitlebarLeftControls: React.FC = () => {
   const clusterRef = React.useRef<HTMLDivElement | null>(null);
 
   const toggleShortcut = formatShortcutForDisplay(getEffectiveShortcutCombo('toggle_sidebar', shortcutOverrides));
-  const isWindowsElectronDesktop = React.useMemo(() => {
-    if (typeof window === 'undefined') {
-      return false;
-    }
-    return Boolean(window.__OPENCHAMBER_ELECTRON__) && window.__OPENCHAMBER_PLATFORM__ === 'win32';
-  }, []);
+  const { usesFramelessChrome, side: windowControlsSide } = useDesktopWindowControlsLayout();
 
   const handleOpenWindowsAppMenu = React.useCallback((event: React.MouseEvent<HTMLButtonElement>) => {
     const rect = event.currentTarget.getBoundingClientRect();
@@ -88,7 +85,11 @@ export const TitlebarLeftControls: React.FC = () => {
       }}
     >
       <div ref={clusterRef} className="flex items-center gap-2">
-        {isWindowsElectronDesktop ? (
+        {usesFramelessChrome && windowControlsSide === 'left' ? (
+          <WindowsWindowControls visible position="left" />
+        ) : null}
+
+        {usesFramelessChrome ? (
           <Tooltip>
             <TooltipTrigger asChild>
               <button