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_enroll_host.py

@@ -0,0 +1,72 @@
+"""POST /swarm/enroll — issue a worker cert bundle and register the host.
+
+Enrollment is master-driven: the controller holds the CA private key,
+generates a fresh worker keypair + CA-signed cert, and returns the full
+bundle to the operator. Bundle delivery to the worker (scp/sshpass/etc.)
+is outside this process's trust boundary.
+
+Rationale: the worker agent speaks ONLY mTLS; there is no pre-auth
+bootstrap endpoint, so nothing to attack before the worker is enrolled.
+"""
+from __future__ import annotations
+
+import uuid as _uuid
+from datetime import datetime, timezone
+
+from fastapi import APIRouter, Depends, HTTPException, status
+
+from decnet.swarm import pki
+from decnet.web.db.repository import BaseRepository
+from decnet.web.dependencies import get_repo
+from decnet.web.router.swarm._schemas import EnrolledBundle, EnrollRequest
+
+router = APIRouter()
+
+
+@router.post(
+    "/enroll",
+    response_model=EnrolledBundle,
+    status_code=status.HTTP_201_CREATED,
+    tags=["Swarm Hosts"],
+)
+async def api_enroll_host(
+    req: EnrollRequest,
+    repo: BaseRepository = Depends(get_repo),
+) -> EnrolledBundle:
+    existing = await repo.get_swarm_host_by_name(req.name)
+    if existing is not None:
+        raise HTTPException(status_code=409, detail=f"Worker '{req.name}' is already enrolled")
+
+    ca = pki.ensure_ca()
+    sans = list({*req.sans, req.address, req.name})
+    issued = pki.issue_worker_cert(ca, req.name, sans)
+
+    # Persist the bundle under ~/.decnet/ca/workers/<name>/ so the master
+    # can replay it if the operator loses the original delivery.
+    bundle_dir = pki.DEFAULT_CA_DIR / "workers" / req.name
+    pki.write_worker_bundle(issued, bundle_dir)
+
+    host_uuid = str(_uuid.uuid4())
+    await repo.add_swarm_host(
+        {
+            "uuid": host_uuid,
+            "name": req.name,
+            "address": req.address,
+            "agent_port": req.agent_port,
+            "status": "enrolled",
+            "client_cert_fingerprint": issued.fingerprint_sha256,
+            "cert_bundle_path": str(bundle_dir),
+            "enrolled_at": datetime.now(timezone.utc),
+            "notes": req.notes,
+        }
+    )
+    return EnrolledBundle(
+        host_uuid=host_uuid,
+        name=req.name,
+        address=req.address,
+        agent_port=req.agent_port,
+        fingerprint=issued.fingerprint_sha256,
+        ca_cert_pem=issued.ca_cert_pem.decode(),
+        worker_cert_pem=issued.cert_pem.decode(),
+        worker_key_pem=issued.key_pem.decode(),
+    )