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_updates/api_list_host_releases.py

@@ -64,6 +64,10 @@ async def _probe_host(host: dict[str, Any]) -> HostReleaseInfo:
     "/hosts",
     response_model=HostReleasesResponse,
     tags=["Swarm Updates"],
+    responses={
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+    },
 )
 async def api_list_host_releases(
     admin: dict = Depends(require_admin),

decnet/web/router/swarm_updates/api_push_update.py

@@ -128,6 +128,13 @@ def _is_expected_connection_drop(exc: BaseException) -> bool:
     "/push",
     response_model=PushUpdateResponse,
     tags=["Swarm Updates"],
+    responses={
+        400: {"description": "Bad Request (malformed JSON body or conflicting host_uuids/all flags)"},
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+        404: {"description": "No matching target hosts or no updater-capable hosts enrolled"},
+        422: {"description": "Request body validation error"},
+    },
 )
 async def api_push_update(
     req: PushUpdateRequest,

decnet/web/router/swarm_updates/api_push_update_self.py

@@ -68,6 +68,13 @@ async def _push_self_one(host: dict[str, Any], tarball: bytes, sha: str) -> Push
     "/push-self",
     response_model=PushUpdateResponse,
     tags=["Swarm Updates"],
+    responses={
+        400: {"description": "Bad Request (malformed JSON body or conflicting host_uuids/all flags)"},
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+        404: {"description": "No matching target hosts or no updater-capable hosts enrolled"},
+        422: {"description": "Request body validation error"},
+    },
 )
 async def api_push_update_self(
     req: PushUpdateRequest,

decnet/web/router/swarm_updates/api_rollback_host.py

@@ -23,6 +23,13 @@ router = APIRouter()
     "/rollback",
     response_model=RollbackResponse,
     tags=["Swarm Updates"],
+    responses={
+        400: {"description": "Bad Request (malformed JSON body or host has no updater bundle)"},
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Insufficient permissions"},
+        404: {"description": "Unknown host, or no previous release slot on the worker"},
+        422: {"description": "Request body validation error"},
+    },
 )
 async def api_rollback_host(
     req: RollbackRequest,