feat(sessions): add detail page, Notification component, and session API improvements

- add SessionDetailPage with breadcrumbs, DescriptionList, status badge, masked token
- add Notification component (info/success/error/warning/note variants) for contextual messages
- use Notification for 404 errors on session and environment detail pages
- add GET /sessions/:id endpoint; sanitize token (head…tail) and strip cookies/localStorage
- change DELETE /sessions/:id to return 204 No Content so client redirect works correctly
- add onRowClick prop to Table for clickable rows; stop propagation on actions column
- update status badges: open=success (green), closed=error (red) on both list and detail

client/src/ui/Notification/Notification.tsx

@@ -0,0 +1,36 @@
+import { AlertCircle, AlertTriangle, CheckCircle2, Info, StickyNote } from 'lucide-react';
+import styles from './Notification.module.css';
+
+export type NotificationVariant = 'info' | 'success' | 'error' | 'warning' | 'note';
+
+export interface NotificationProps {
+  variant?: NotificationVariant;
+  title?: string;
+  children: React.ReactNode;
+  className?: string;
+}
+
+const ICONS: Record<NotificationVariant, React.ReactNode> = {
+  info:    <Info size={16} />,
+  success: <CheckCircle2 size={16} />,
+  error:   <AlertCircle size={16} />,
+  warning: <AlertTriangle size={16} />,
+  note:    <StickyNote size={16} />,
+};
+
+export function Notification({
+  variant = 'info',
+  title,
+  children,
+  className,
+}: NotificationProps) {
+  return (
+    <div className={[styles.notification, styles[variant], className].filter(Boolean).join(' ')}>
+      <span className={styles.icon}>{ICONS[variant]}</span>
+      <div className={styles.body}>
+        {title && <p className={styles.title}>{title}</p>}
+        <p className={styles.message}>{children}</p>
+      </div>
+    </div>
+  );
+}