chore(types): enable warn_return_any and cast all no-any-return sites

Turn on mypy warn_return_any (pyproject) and resolve the 84 resulting
[no-any-return] errors across 43 files with typing.cast() at the return
sites — runtime no-ops that make the declared return type explicit where a
dependency (SQLAlchemy scalar/first/one, httpx .json(), subprocess, docker
SDK) hands back Any. No behavior change: no DTO/table field types altered, no
validation/coercion calls added, every cast reflects the true runtime type.

Locks in return-type strictness so the class of bug where a function silently
widens to Any can't regress. mypy decnet/ clean; adversarially verified
behavior-preserving (84 casts 1:1 with prior returns).

Bump tornado 6.5.5 -> 6.5.7 (CVE-2026-49854, transitive via snakeviz).

decnet/web/db/sqlmodel_repo/topology/mutations.py

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from datetime import datetime, timezone
-from typing import Any, Optional
+from typing import Any, Optional, cast
 
 import orjson
 from sqlalchemy import asc, desc, select, text
@@ -102,7 +102,7 @@ class TopologyMutationsMixin(_MixinBase):
             _ = now
             if row is None:
                 return None
-            return row.model_dump(mode="json")
+            return cast(dict[str, Any], row.model_dump(mode="json"))
 
     async def mark_mutation_applied(self, mutation_id: str) -> None:
         async with self._session() as session: