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/SimpleInput.js

@@ -34,12 +34,12 @@ export function SimpleInput({ sessionId, status, onRespond }) {
         onBlur=${() => setFocused(false)}
         placeholder="Send a message..."
         rows="1"
-        class="flex-1 resize-none overflow-hidden rounded-xl border border-selection/75 bg-bg/70 px-3 py-2 text-sm text-fg placeholder:text-dim focus:outline-none"
+        class="flex-1 resize-none overflow-hidden rounded-xl border border-selection/75 bg-bg/70 px-3 py-2 text-sm text-fg transition-colors duration-150 placeholder:text-dim focus:outline-none"
         style=${{ minHeight: '38px', maxHeight: '150px', borderColor: focused ? meta.borderColor : undefined }}
       />
       <button
         type="submit"
-        class="shrink-0 rounded-xl px-3 py-2 text-sm font-medium transition-all hover:-translate-y-0.5 hover:brightness-110"
+        class="shrink-0 rounded-xl px-3 py-2 text-sm font-medium transition-[transform,filter] duration-150 hover:-translate-y-0.5 hover:brightness-110"
         style=${{ backgroundColor: meta.borderColor, color: '#0a0f18' }}
       >
         Send