feat(client): add UI kit, data layer, app shell, and Table component

- design token system (Atlantis, Kimberly, Powder Ash palette)
- Button, Badge, Input, Select, Card, SidePanel, Breadcrumbs components
- generic typed Table<T> component with loading/empty states
- API data layer: typed fetch client for environments, keys, sessions, scenarios
- Vite dev proxy targeting server on port 13000
- App shell with SidePanel nav and four entity pages (Environments, Keys, Sessions, Scenarios)
- Storybook config with dark/light theme toggle and a11y addon

client/.storybook/main.ts

@@ -0,0 +1,26 @@
+import type { StorybookConfig } from '@storybook/react-vite';
+
+import { dirname } from "path"
+
+import { fileURLToPath } from "url"
+
+/**
+* This function is used to resolve the absolute path of a package.
+* It is needed in projects that use Yarn PnP or are set up within a monorepo.
+*/
+function getAbsolutePath(value: string) {
+  return dirname(fileURLToPath(import.meta.resolve(`${value}/package.json`)))
+}
+const config: StorybookConfig = {
+  "stories": [
+    "../src/**/*.mdx",
+    "../src/**/*.stories.@(js|jsx|mjs|ts|tsx)"
+  ],
+  "addons": [
+    getAbsolutePath('@storybook/addon-vitest'),
+    getAbsolutePath('@storybook/addon-a11y'),
+    getAbsolutePath('@storybook/addon-docs')
+  ],
+  "framework": getAbsolutePath('@storybook/react-vite')
+};
+export default config;

client/.storybook/preview.tsx

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+import React from 'react'
+import type { Preview } from '@storybook/react-vite'
+import '../src/ui/tokens.css'
+
+const preview: Preview = {
+  globalTypes: {
+    theme: {
+      name: 'Theme',
+      description: 'Color theme',
+      defaultValue: 'light',
+      toolbar: {
+        icon: 'circlehollow',
+        items: [
+          { value: 'light', icon: 'sun', title: 'Light' },
+          { value: 'dark',  icon: 'moon', title: 'Dark' },
+        ],
+        dynamicTitle: true,
+      },
+    },
+  },
+  decorators: [
+    (Story, context) => {
+      const theme = (context.globals['theme'] as string) ?? 'light'
+      document.documentElement.setAttribute('data-theme', theme)
+      return (
+        <div style={{ background: 'var(--color-bg)', minHeight: '100vh', padding: 0 }}>
+          <Story />
+        </div>
+      )
+    },
+  ],
+  parameters: {
+    controls: {
+      matchers: {
+        color: /(background|color)$/i,
+        date: /Date$/i,
+      },
+    },
+    a11y: {
+      test: 'todo',
+    },
+  },
+}
+
+export default preview