feat(client): add ContextMenu component, environment cards, detail page, and breadcrumbs

- add ContextMenu component with click-outside/Escape dismiss, align prop, and danger variant
- replace EnvironmentsPage table with responsive card grid
- add cog button to each card opening a context menu with view and delete actions
- add EnvironmentDetailPage at /environments/:id with meta grid, URLs card, and delete
- add Breadcrumbs to all pages; detail page uses two-item trail with delete button inline
- add Table stories for pagination and Timestamp column

client/src/pages/SessionsPage.tsx

@@ -2,7 +2,7 @@ import { useCallback, useEffect, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { sessions } from '../api';
 import type { Session } from '../api';
-import { Badge, Button, Table, type TableColumn, Timestamp } from '../ui';
+import { Badge, Breadcrumbs, Button, Table, type TableColumn, Timestamp } from '../ui';
 import styles from './Page.module.css';
 
 export function SessionsPage() {
@@ -61,7 +61,7 @@ export function SessionsPage() {
 
   return (
     <div>
-      <h1 className={styles.heading}>{t('sessions.title')}</h1>
+      <Breadcrumbs items={[{ label: t('sessions.title') }]} className={styles.breadcrumbs} />
       {error && <p className={styles.error}>{error}</p>}
       <Table
         columns={columns}