fix: disable frontend service until Phase 4, simplify Caddy proxy

Frontend SvelteKit build has dependency conflicts (Svelte 5 + Vite 8).
Phase 0 setup wizard is served by FastAPI/Jinja2, no frontend needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Caddyfile

@@ -1,22 +1,7 @@
 pkm.hyungi.net {
-    # API + OpenAPI 문서
-    handle /api/* {
-        reverse_proxy fastapi:8000
-    }
-    handle /docs {
-        reverse_proxy fastapi:8000
-    }
-    handle /openapi.json {
-        reverse_proxy fastapi:8000
-    }
-    handle /health {
-        reverse_proxy fastapi:8000
-    }
-
-    # 프론트엔드
-    handle {
-        reverse_proxy frontend:3000
-    }
+    # Phase 0~3: FastAPI가 모든 요청 처리 (셋업 위자드 포함)
+    # Phase 4: 프론트엔드 분리 시 경로별 라우팅 추가
+    reverse_proxy fastapi:8000
 }
 
 # Synology Office 프록시