refactor: 仓库结构扁平化 + PHP前端合并到Nexus仓库

- 将 Nexus/Nexus/* 移到仓库根目录（消除双层嵌套）
- 删除旧的多层空壳目录 (server/, web/, agent/, deploy/, docs/)
- 将PHP前端 (web/) 合并进Nexus仓库 — 统一管理
- 部署时 git clone Nexus 仓库即可，不再需要两个仓库

目录结构：
  server/     ← Python FastAPI后端
  web/        ← PHP前端 (install.php, config.php, etc)
  deploy/     ← Supervisor + Shell健康检查
  docs/       ← 部署文档
  tests/      ← 测试
  .env        ← 不在git中 (install.php生成)
  .gitignore  ← 排除 .env, SECRETS.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/application/services/server_service.py

@@ -0,0 +1,95 @@
+"""Nexus — Server Service (Business logic for server management)
+Application layer — orchestrates Repository + SSH pool + Redis cache.
+"""
+
+import asyncio
+import json
+import logging
+from typing import Optional, List, Dict
+
+from server.domain.models import Server, SyncLog
+from server.domain.repositories import ServerRepository, SyncLogRepository
+from server.infrastructure.ssh.pool import SSHConfig, exec_command
+from server.infrastructure.redis.client import get_redis
+
+logger = logging.getLogger("nexus.server_service")
+
+
+class ServerService:
+    """Business logic for server CRUD, health check, and push operations"""
+
+    def __init__(self, server_repo: ServerRepository, sync_log_repo: SyncLogRepository):
+        self.server_repo = server_repo
+        self.sync_log_repo = sync_log_repo
+
+    async def list_servers(self, category: Optional[str] = None) -> List[Server]:
+        """List all servers, optionally filtered by category"""
+        if category:
+            return await self.server_repo.get_by_category(category)
+        return await self.server_repo.get_all()
+
+    async def get_server(self, id: int) -> Optional[Server]:
+        return await self.server_repo.get_by_id(id)
+
+    async def create_server(self, server: Server) -> Server:
+        return await self.server_repo.create(server)
+
+    async def update_server(self, server: Server) -> Server:
+        return await self.server_repo.update(server)
+
+    async def delete_server(self, id: int) -> bool:
+        return await self.server_repo.delete(id)
+
+    async def update_heartbeat(self, id: int, data: dict) -> None:
+        """Process Agent heartbeat data"""
+        is_online = data.get("is_online", True)
+        system_info = json.dumps(data.get("system_info", {}))
+        agent_version = data.get("agent_version", "")
+        await self.server_repo.update_heartbeat(id, is_online, system_info, agent_version)
+
+    async def check_all_servers(self, server_ids: List[int]) -> Dict[int, dict]:
+        """Check health of multiple servers via Agent API (no SSH)"""
+        results = {}
+        # TODO: Use httpx to call each Agent's /health endpoint
+        for id in server_ids:
+            server = await self.server_repo.get_by_id(id)
+            if server and server.is_online:
+                results[id] = {"status": "online", "system_info": json.loads(server.system_info or "{}")}
+            elif server:
+                results[id] = {"status": "offline"}
+            else:
+                results[id] = {"status": "not_found"}
+        return results
+
+    async def push_to_servers(
+        self,
+        server_ids: List[int],
+        source_path: str,
+        sync_mode: str = "incremental",
+        operator: str = "admin",
+    ) -> Dict[int, SyncLog]:
+        """Push files to multiple servers in batches"""
+        results = {}
+        servers = []
+        for id in server_ids:
+            server = await self.server_repo.get_by_id(id)
+            if server:
+                servers.append(server)
+
+        # TODO: Implement batch push with asyncio.Semaphore(10)
+        # batch_size=50, interval=30s
+        for server in servers:
+            target_path = server.target_path or f"/www/wwwroot/"
+            log = SyncLog(
+                server_id=server.id,
+                source_path=source_path,
+                target_path=target_path,
+                trigger_type="batch",
+                operator=operator,
+                status="pending",
+                sync_mode=sync_mode,
+            )
+            log = await self.sync_log_repo.create(log)
+            results[server.id] = log
+
+        return results