feat: 新增预算详情模态框、交易表单、小猪罐功能，并支持生成预算洞察。

src/pages/Budget/Budget.css

@@ -300,4 +300,45 @@
   .piggy-banks-list {
     grid-template-columns: repeat(3, 1fr);
   }
+
+  .budgets-list,
+  .piggy-banks-list {
+    grid-template-columns: repeat(3, 1fr);
+  }
+}
+
+/* Generic Modal for Budget Page */
+.budget-modal-overlay {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  background: rgba(0, 0, 0, 0.5);
+  backdrop-filter: blur(4px);
+  z-index: 1100;
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  padding: var(--spacing-md);
+  animation: fadeIn 0.2s ease-out;
+}
+
+.budget-modal-content {
+  width: 100%;
+  max-width: 500px;
+  background: transparent;
+  animation: scaleIn 0.3s cubic-bezier(0.16, 1, 0.3, 1);
+}
+
+@keyframes scaleIn {
+  from {
+    opacity: 0;
+    transform: scale(0.95);
+  }
+
+  to {
+    opacity: 1;
+    transform: scale(1);
+  }
 }