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/electron/scripts/rebuild-native.mjs

@@ -6,6 +6,7 @@ import { execFileSync } from 'node:child_process';
 import { fileURLToPath } from 'node:url';
 import { createRequire } from 'node:module';
 import { rebuild } from '@electron/rebuild';
+import { resolveTargetArchitecture } from './target-architecture.mjs';
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
@@ -16,6 +17,7 @@ const require = createRequire(import.meta.url);
 
 const electronPkg = require('electron/package.json');
 const electronVersion = electronPkg.version;
+const targetArchitecture = resolveTargetArchitecture();
 
 const copyDirectory = async (src, dst) => {
   await fsp.mkdir(dst, { recursive: true });
@@ -142,7 +144,7 @@ try {
     buildPath: rebuildPath.buildPath,
     electronVersion,
     force: true,
-    arch: process.env.ELECTRON_BUILDER_ARCH || process.arch,
+    arch: targetArchitecture.electronBuilder,
     onlyModules: ['better-sqlite3', 'node-pty', 'bun-pty'],
   });
 } finally {