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/OptionButton.js

@@ -4,7 +4,7 @@ export function OptionButton({ number, label, description, onClick }) {
   return html`
     <button
       onClick=${onClick}
-      class="group w-full rounded-xl border border-selection/70 bg-surface2/55 p-3.5 text-left transition-all duration-200 hover:-translate-y-0.5 hover:border-starting/55 hover:bg-surface2/90 hover:shadow-halo"
+      class="group w-full rounded-xl border border-selection/70 bg-surface2/55 p-3.5 text-left transition-[transform,border-color,background-color,box-shadow] duration-200 hover:-translate-y-0.5 hover:border-starting/55 hover:bg-surface2/90 hover:shadow-halo"
     >
       <div class="flex items-baseline gap-2.5">
         <span class="font-mono text-starting">${number}.</span>