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/observations.py

@@ -21,7 +21,7 @@ not validate values — that happens at construction time by the BEHAVE
 from __future__ import annotations
 
 import uuid as _uuid
-from typing import Any, Optional
+from typing import Any, Optional, cast
 
 from sqlalchemy import desc, func, select
 from sqlmodel import col
@@ -85,7 +85,7 @@ class ObservationsMixin(_MixinBase):
                 row_data = {**data, "id": row_id}
                 session.add(ObservationRow(**row_data))
             await session.commit()
-            return row_id
+            return cast(str, row_id)
 
     async def latest_observation_per_primitive(
         self, attacker_uuid: str,
@@ -178,7 +178,7 @@ class ObservationsMixin(_MixinBase):
             row = (await session.execute(stmt)).scalar_one_or_none()
             if not row:
                 return None
-            return row.model_dump(mode="json")
+            return cast(dict[str, Any], row.model_dump(mode="json"))
 
     async def observations_for_identity_primitive(
         self, identity_uuid: str, primitive: str,