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_decommission_host.py

@@ -0,0 +1,46 @@
+"""DELETE /swarm/hosts/{uuid} — decommission a worker.
+
+Removes the DeckyShard rows bound to the host (portable cascade — MySQL
+and SQLite both honor it via the repo layer), deletes the SwarmHost row,
+and best-effort-cleans the per-worker bundle directory on the master.
+"""
+from __future__ import annotations
+
+import pathlib
+
+from fastapi import APIRouter, Depends, HTTPException, status
+
+from decnet.web.db.repository import BaseRepository
+from decnet.web.dependencies import get_repo
+
+router = APIRouter()
+
+
+@router.delete(
+    "/hosts/{uuid}",
+    status_code=status.HTTP_204_NO_CONTENT,
+    tags=["Swarm Hosts"],
+)
+async def api_decommission_host(
+    uuid: str,
+    repo: BaseRepository = Depends(get_repo),
+) -> None:
+    row = await repo.get_swarm_host_by_uuid(uuid)
+    if row is None:
+        raise HTTPException(status_code=404, detail="host not found")
+
+    await repo.delete_decky_shards_for_host(uuid)
+    await repo.delete_swarm_host(uuid)
+
+    # Best-effort bundle cleanup; if the dir was moved manually, don't fail.
+    bundle_dir = pathlib.Path(row.get("cert_bundle_path") or "")
+    if bundle_dir.is_dir():
+        for child in bundle_dir.iterdir():
+            try:
+                child.unlink()
+            except OSError:
+                pass
+        try:
+            bundle_dir.rmdir()
+        except OSError:
+            pass