refactor: organize frontend components into features/ directories

Moved 43 component files into 9 feature domains:
- features/git/ — commit-dialog, commit-panel, file-editor, git-mount-editor,
  git-toolbar, merge-dialog
- features/project/ — repositories-settings-tab, repository-create-dialog
- features/terminal/ — special-keys-panel, special-keys-strip,
  terminal-session-tabs, terminal
- features/workspace/ — workspace-card, workspace-create-form,
  workspace-header, workspace-instance-chips
- features/session/ — create-session-form, session-card, session-list
- features/tool/ — instance-list, manifest-editor, start-tool-fab,
  start-tool-modal, tool-starter, tools-bottom-sheet
- features/notification/ — event-toast-bridge, notification-center,
  notification-item
- features/settings/ — settings-tab-layout
- features/mobile/ — mobile-action-sheet, mobile-detail-view, mobile-edit-view,
  mobile-fab, mobile-list-view, mobile-nav, mobile-page-header,
  mobile-terminal-header, mobile-terminal-wrapper

Updated all imports across pages and components.
Root components/ now only contains generic UI pieces:
app-shell, code-editor, data-states, icon, protected-route, syntax-highlighter.

Quality gates: verified no remaining old imports.

apps/web/src/components/features/notification/notification-item.tsx

@@ -0,0 +1,64 @@
+import { Icon } from "./icon";
+import { formatRelativeTime } from "../utils/time";
+import type { NotificationItem as NotificationItemType } from "../api/notifications";
+
+export interface NotificationItemProps {
+	notification: NotificationItemType;
+	onMarkRead: (id: string) => void;
+	onDismiss: (id: string) => void;
+}
+
+import type { IconName } from "../utils/icons";
+
+const severityIconMap: Record<string, IconName> = {
+	info: "info",
+	warning: "warning",
+	error: "error",
+	success: "success",
+};
+
+export function NotificationItem({
+	notification,
+	onMarkRead,
+	onDismiss,
+}: NotificationItemProps) {
+	const isUnread = notification.read_at === null;
+	const iconName = severityIconMap[notification.severity] ?? "info";
+
+	return (
+		<li
+			role="listitem"
+			className={`notification-item ${isUnread ? "notification-item--unread" : "notification-item--read"}`}
+		>
+			<div className="notification-item-icon">
+				<Icon name={iconName} size="md" />
+			</div>
+			<div className="notification-item-content">
+				<div className="notification-item-title">{notification.title}</div>
+				<div className="notification-item-time">
+					{formatRelativeTime(notification.created_at)}
+				</div>
+			</div>
+			<div className="notification-item-actions">
+				{isUnread && (
+					<button
+						type="button"
+						className="notification-item-action"
+						onClick={() => onMarkRead(notification.id)}
+						aria-label="Mark read"
+					>
+						Mark read
+					</button>
+				)}
+				<button
+					type="button"
+					className="notification-item-action"
+					onClick={() => onDismiss(notification.id)}
+					aria-label="Dismiss"
+				>
+					Dismiss
+				</button>
+			</div>
+		</li>
+	);
+}