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/webhooks.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
 
 from sqlalchemy import select, update
 from sqlmodel import col
@@ -65,7 +65,7 @@ class WebhooksMixin(_MixinBase):
                 .values(**patch)
             )
             await session.commit()
-            return result.rowcount > 0
+            return cast(bool, result.rowcount > 0)
 
     async def delete_webhook_subscription(self, uuid: str) -> bool:
         async with self._session() as session: