fix: resolve 8 review/security issues (SPRINT-016 hotfix)

Security:
- JwtGuard + RoleGuard on all sisters endpoints
- Admin-only access for config/sessions/subagents/activity
- ThrottlerGuard on /auth/refresh
- HttpOnly SameSite cookies + CSRF (replaces localStorage)

Code Quality:
- Per-sister draft input (Record<SisterName, string>)
- crypto.randomUUID for optimistic message ids (dedupe ready)
- Polling disabled while WebSocket connected
- SVG keyboard accessibility (role/tabIndex/onKeyDown)

backend/src/events/events.gateway.ts

@@ -11,6 +11,7 @@ import { Logger } from '@nestjs/common';
 import { JwtService } from '@nestjs/jwt';
 import { ConfigService } from '@nestjs/config';
 import { OnEvent } from '@nestjs/event-emitter';
+import { ACCESS_TOKEN_COOKIE, parseCookieHeader } from '../auth/auth-cookies';
 
 interface SocketUserPayload {
   username?: string;
@@ -50,12 +51,17 @@ export class EventsGateway
 
   handleConnection(client: SocketWithUser) {
     // JWT 인증 필수 — 토큰 없거나 유효하지 않으면 disconnect
+    const authHeader = client.handshake.headers.authorization;
+    const tokenFromHeader = Array.isArray(authHeader)
+      ? authHeader[0]?.replace('Bearer ', '')
+      : authHeader?.replace('Bearer ', '');
+    const tokenFromCookie = parseCookieHeader(client.handshake.headers.cookie)[
+      ACCESS_TOKEN_COOKIE
+    ];
     const token =
-      (client.handshake.auth?.token as string) ??
-      (client.handshake.headers.authorization as string)?.replace(
-        'Bearer ',
-        '',
-      );
+      (client.handshake.auth?.token as string | undefined) ??
+      tokenFromHeader ??
+      tokenFromCookie;
 
     if (!token) {
       this.logger.debug(`WS rejected (no token): ${client.id}`);