feat(Loader): create loader component with spinner and optional message

src/shared/ui/Loader/Loader.stories.svelte

@@ -0,0 +1,33 @@
+<script module>
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import Loader from './Loader.svelte';
+
+const { Story } = defineMeta({
+    title: 'Shared/Loader',
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component: 'Spinner with optional message',
+            },
+            story: { inline: false }, // Render stories in iframe for state isolation
+        },
+    },
+    argTypes: {
+        message: {
+            control: 'text',
+            description: 'Optional message to display',
+            defaultValue: 'analyzing_data',
+        },
+        size: {
+            control: 'number',
+            description: 'Size of the spinner',
+            defaultValue: 20,
+        },
+    },
+});
+</script>
+
+<Story name="Default">
+    <Loader />
+</Story>