fix: improve note interactions and markdown LaTeX support

## Bug Fixes

### Note Card Actions
- Fix broken size change functionality (missing state declaration)
- Implement React 19 useOptimistic for instant UI feedback
- Add startTransition for non-blocking updates
- Ensure smooth animations without page refresh
- All note actions now work: pin, archive, color, size, checklist

### Markdown LaTeX Rendering
- Add remark-math and rehype-katex plugins
- Support inline equations with dollar sign syntax
- Support block equations with double dollar sign syntax
- Import KaTeX CSS for proper styling
- Equations now render correctly instead of showing raw LaTeX

## Technical Details

- Replace undefined currentNote references with optimistic state
- Add optimistic updates before server actions for instant feedback
- Use router.refresh() in transitions for smart cache invalidation
- Install remark-math, rehype-katex, and katex packages

## Testing

- Build passes successfully with no TypeScript errors
- Dev server hot-reloads changes correctly

keep-notes/components/label-manager.tsx

@@ -102,7 +102,32 @@ export function LabelManager({ existingLabels, onUpdate }: LabelManagerProps) {
           Labels
         </Button>
       </DialogTrigger>
-      <DialogContent className="max-w-md">
+      <DialogContent
+        className="max-w-md"
+        onInteractOutside={(event) => {
+          // Prevent dialog from closing when interacting with Sonner toasts
+          const target = event.target as HTMLElement;
+
+          const isSonnerElement =
+            target.closest('[data-sonner-toast]') ||
+            target.closest('[data-sonner-toaster]') ||
+            target.closest('[data-icon]') ||
+            target.closest('[data-content]') ||
+            target.closest('[data-description]') ||
+            target.closest('[data-title]') ||
+            target.closest('[data-button]');
+
+          if (isSonnerElement) {
+            event.preventDefault();
+            return;
+          }
+
+          if (target.getAttribute('data-sonner-toaster') !== null) {
+            event.preventDefault();
+            return;
+          }
+        }}
+      >
         <DialogHeader>
           <DialogTitle>Manage Labels</DialogTitle>
           <DialogDescription>