fix: make stats panel scrollable when content overflows

The stats panel in StatusBar could grow too long when all sections
(Tools Used, Historical Costs, Budget tracking) were expanded, causing
content to overflow off the bottom of the screen.

Added max-height and overflow-y-auto to the stats container to ensure
it stays within the viewport and can be scrolled when needed.

Fixes: #136

src/lib/components/StatusBar.svelte

@@ -696,7 +696,7 @@
   <!-- svelte-ignore a11y_click_events_have_key_events -->
   <!-- svelte-ignore a11y_no_static_element_interactions -->
   <div class="fixed inset-0 z-40" onclick={() => (showStats = false)}></div>
-  <div class="fixed top-14 right-4 z-50">
+  <div class="fixed top-14 right-4 z-50 max-h-[calc(100vh-4rem)] overflow-y-auto">
     <StatsDisplay
       onRequestSummary={handleCompactConversation}
       onStartFreshWithContext={handleStartFreshWithContext}