perf(dashboard): optimize CSS transitions and add entrance animations

Performance and polish improvements across dashboard components:

Transition optimizations (reduces reflow/repaint overhead):
- OptionButton: transition-all → transition-[transform,border-color,
  background-color,box-shadow]
- QuestionBlock: Add transition-colors to textarea, transition-all →
  transition-[transform,filter] on send button
- SimpleInput: Same pattern as QuestionBlock
- Sidebar: transition-all → transition-colors for project buttons

Animation additions:
- App: Add animate-fade-in-up to loading and error state containers
- MessageBubble: Make fade-in-up animation conditional on non-compact
  mode to avoid animation spam in card preview

Using specific transition properties instead of transition-all tells
the browser exactly which properties to watch, avoiding unnecessary
style recalculation on unrelated property changes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dashboard/components/App.js

@@ -347,11 +347,11 @@ export function App() {
 
       <main class="px-6 pb-6 pt-6">
         ${loading ? html`
-          <div class="glass-panel flex items-center justify-center rounded-2xl py-24">
+          <div class="glass-panel animate-fade-in-up flex items-center justify-center rounded-2xl py-24">
             <div class="font-mono text-dim">Loading sessions...</div>
           </div>
         ` : error ? html`
-          <div class="glass-panel flex items-center justify-center rounded-2xl py-24">
+          <div class="glass-panel animate-fade-in-up flex items-center justify-center rounded-2xl py-24">
             <div class="text-center">
               <p class="mb-2 font-display text-lg text-attention">Failed to connect to API</p>
               <p class="font-mono text-sm text-dim">${error}</p>