M19: Move sidebarCollapsed from localStorage to electron-store

Sidebar collapsed state was an orphan in localStorage -- not backed up,
lost on portable installs, and inconsistent with every other preference.

Added sidebarCollapsed: boolean to the Settings type and DEFAULT_SETTINGS,
wired it through applySettings' boolean branch, and updated the renderer
store / main.tsx mock defaults. App.tsx now drives the toggle via
updateSettings({ sidebarCollapsed }) instead of localStorage.

typecheck + 242 tests + eslint green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/shared/ipc.ts

@@ -553,6 +553,8 @@ export interface Settings {
   minimizeToTray: boolean
   /** launch AeroFetch automatically when the user signs in to Windows */
   launchAtStartup: boolean
+  /** whether the navigation sidebar is collapsed to icon-only mode */
+  sidebarCollapsed: boolean
   /**
    * Optional Gitea access token for the in-app updater. Empty = anonymous (works
    * only where the release repo allows anonymous access). When the release repo