feat(kon): collapsible sidebar — toggle with [ key, auto-collapse below 900px, icons-only mode

- Add sidebarCollapsed to settings defaults (persists via localStorage on saveSettings)
- Sidebar collapses to 48px icons-only view with smooth 200ms transition
- Toggle button (chevron) at top of nav; [ keyboard shortcut in layout (input-safe)
- Auto-collapse on window resize below 900px (checked on mount and on resize event)
- Titlebar left spacer tracks sidebar width reactively (48px / 210px)
- All labels, profile selector, status text hidden in collapsed mode; nav items show tooltips via title attribute

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/components/Titlebar.svelte

@@ -1,5 +1,6 @@
 <script>
   import { getCurrentWindow } from "@tauri-apps/api/window";
+  import { settings } from "$lib/stores/page.svelte.js";
 
   let maximised = $state(false);
 
@@ -38,7 +39,10 @@
   data-tauri-drag-region
 >
   <!-- Left spacer: aligns with sidebar width -->
-  <div class="w-[210px] min-w-[210px]" data-tauri-drag-region></div>
+  <div
+    class="transition-all duration-200 {settings.sidebarCollapsed ? 'w-[48px] min-w-[48px]' : 'w-[210px] min-w-[210px]'}"
+    data-tauri-drag-region
+  ></div>
 
   <!-- Centre: drag area -->
   <div class="flex-1" data-tauri-drag-region></div>