refactor(swarm): one file per endpoint, matching existing router layout

Splits the three grouped router files into eight api_<verb>_<resource>.py
modules under decnet/web/router/swarm/ to match the convention used by
router/fleet/ and router/config/. Shared request/response models live in
_schemas.py. Keeps each endpoint easy to locate and modify without
stepping on siblings.

decnet/web/router/swarm/api_list_hosts.py

@@ -0,0 +1,21 @@
+"""GET /swarm/hosts — list enrolled workers, optionally filtered by status."""
+from __future__ import annotations
+
+from typing import Optional
+
+from fastapi import APIRouter, Depends
+
+from decnet.web.db.repository import BaseRepository
+from decnet.web.dependencies import get_repo
+from decnet.web.router.swarm._schemas import SwarmHostView
+
+router = APIRouter()
+
+
+@router.get("/hosts", response_model=list[SwarmHostView], tags=["Swarm Hosts"])
+async def api_list_hosts(
+    host_status: Optional[str] = None,
+    repo: BaseRepository = Depends(get_repo),
+) -> list[SwarmHostView]:
+    rows = await repo.list_swarm_hosts(host_status)
+    return [SwarmHostView(**r) for r in rows]