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/orchestrator/scheduler.py

@@ -20,7 +20,7 @@ import json
 import secrets
 from dataclasses import dataclass
 from datetime import datetime, timezone
-from typing import Any, Optional, Sequence
+from typing import Any, Optional, Sequence, cast
 
 from decnet.realism import personas_pool
 from decnet.realism.personas import EmailPersona, parse_personas
@@ -256,7 +256,7 @@ def _persona_by_name(
     for decky in enriched:
         for persona in decky.get("_realism_personas") or []:
             if persona.name == name:
-                return persona
+                return cast(EmailPersona, persona)
     return None