feat(sprint-008): 실시간 자매 정보/아바타/설정 DB 연동

- TASK-028: /api/sisters/:name/system 추가, 자매 페이지 uptime/cpu/memory/disk 실시간화
- TASK-029: /api/sisters/:name/avatar 추가, SSH avatar fetch + 5분 캐시 + SVG fallback
- TASK-030: SystemSettings 모델 + /api/admin/settings GET/PUT + FE settings DB 연동/토스트
- TASK-031 일부: 대시보드/자매/설정 스켈레톤 UI + 에러 fallback
- 30초 자매 상태 websocket 브로드캐스트 시작

테스트 26/26 pass, build 성공

backend/src/sisters/sisters.controller.ts

@@ -1,14 +1,17 @@
-import { Controller, Get, Param } from '@nestjs/common';
+import { Controller, Get, Param, Res } from '@nestjs/common';
+import type { Response } from 'express';
 import { SistersService } from './sisters.service';
 import { SisterDetailService } from './sister-detail.service';
 import { SisterNamePipe } from '../common/sister-name.pipe';
 import type { SisterName } from '../common/sister-name.pipe';
+import { AvatarService } from './avatar.service';
 
 @Controller('api/sisters')
 export class SistersController {
   constructor(
     private readonly sistersService: SistersService,
     private readonly sisterDetail: SisterDetailService,
+    private readonly avatarService: AvatarService,
   ) {}
 
   @Get()
@@ -16,6 +19,27 @@ export class SistersController {
     return this.sistersService.getAllSistersStatus();
   }
 
+  @Get(':name/system')
+  async getSystemInfo(@Param('name', SisterNamePipe) name: SisterName) {
+    return this.sistersService.getSystemInfo(name as SisterName);
+  }
+
+  @Get(':name/avatar')
+  async getAvatar(
+    @Param('name', SisterNamePipe) name: SisterName,
+    @Res() res: Response,
+  ) {
+    const sister = await this.sistersService.findByName(name as SisterName);
+    if (!sister) {
+      return res.status(404).json({ message: 'Sister not found' });
+    }
+
+    const avatar = await this.avatarService.getAvatar(sister);
+    res.setHeader('Content-Type', avatar.contentType);
+    res.setHeader('Cache-Control', 'public, max-age=300');
+    return res.send(avatar.data);
+  }
+
   @Get(':name/config')
   async getSisterConfig(@Param('name', SisterNamePipe) name: SisterName) {
     return this.sisterDetail.getSisterConfig(name as SisterName);