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/MessageBubble.js

@@ -17,7 +17,7 @@ export function MessageBubble({ msg, userBg, compact = false, formatTime }) {
   const maxW = compact ? 'max-w-[92%]' : 'max-w-[86%]';
 
   return html`
-    <div class="flex ${isUser ? 'justify-end' : 'justify-start'} animate-fade-in-up">
+    <div class="flex ${isUser ? 'justify-end' : 'justify-start'} ${compact ? '' : 'animate-fade-in-up'}">
       <div
         class="${maxW} rounded-2xl ${pad} ${
           isUser