refactor: optimize reactive variable updates and parsing

- Replace `scanDeclareBlocks` with `parseDeclareCsv` in block processor
- Add error handling for declare block parsing
- Optimize `ReactiveVariableManager` by pre-computing variable keys
- Store template text and keys in data attributes for faster updates
- Adjust `VariableView` popup width via CSS class

src/components/journal/VariableView.tsx

@@ -90,7 +90,7 @@ const VariableRow: Component<{
 
       {/* Hover popup */}
       <Show when={hasPopup() && hovered()}>
-        <div class="absolute right-0 top-full mt-1 z-50 bg-white border border-gray-200 rounded-md shadow-lg p-2 min-w-[180px] text-xs">
+        <div class="absolute right-0 top-full mt-1 z-50 bg-white border border-gray-200 rounded-md shadow-lg p-2 min-w-45 text-xs">
           {/* Declaration expression */}
           <Show when={declExpr()}>
             <div class="mb-1">