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/stores/page.svelte.js

@@ -32,6 +32,7 @@ const defaults = {
   saveAudio: false,
   outputFolder: "",
   globalHotkey: "Ctrl+Shift+R",
+  sidebarCollapsed: false,
 };
 
 function loadSettings() {