fix(api): document missing HTTP status codes on router endpoints

Schemathesis was failing CI on routes that returned status codes not
declared in their OpenAPI responses= dicts. Adds the missing codes
across swarm_updates, swarm_mgmt, swarm, fleet and attackers routers.

Also adds 400 to every POST/PUT/PATCH that accepts a JSON body —
Starlette returns 400 on malformed/non-UTF8 bodies before FastAPI's
422 validation runs, which schemathesis fuzzing trips every time.

No handler logic changed.

decnet/web/router/swarm_mgmt/api_decommission_host.py

@@ -24,6 +24,12 @@ router = APIRouter()
     "/hosts/{uuid}",
     status_code=status.HTTP_204_NO_CONTENT,
     tags=["Swarm Management"],
+    responses={
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+        404: {"description": "Host not found"},
+        422: {"description": "Path parameter validation error"},
+    },
 )
 async def decommission_host(
     uuid: str,

decnet/web/router/swarm_mgmt/api_enroll_bundle.py

@@ -322,6 +322,13 @@ def _render_bootstrap(
     response_model=EnrollBundleResponse,
     status_code=status.HTTP_201_CREATED,
     tags=["Swarm Management"],
+    responses={
+        400: {"description": "Bad Request (malformed JSON body)"},
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+        409: {"description": "A worker with this name is already enrolled"},
+        422: {"description": "Request body validation error"},
+    },
 )
 async def create_enroll_bundle(
     req: EnrollBundleRequest,

decnet/web/router/swarm_mgmt/api_teardown_host.py

@@ -115,6 +115,13 @@ async def _run_teardown(
     response_model=TeardownHostResponse,
     status_code=status.HTTP_202_ACCEPTED,
     tags=["Swarm Management"],
+    responses={
+        400: {"description": "Bad Request (malformed JSON body)"},
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+        404: {"description": "Host not found"},
+        422: {"description": "Request body or path parameter validation error"},
+    },
 )
 async def teardown_host(
     uuid: str,