fix(types): P2 — wire _MixinBase + col() across sqlmodel_repo; suppress pydantic/SQLModel column typing false positives

- Add _MixinBase abstract class to _helpers.py: declares _session(),
  _deserialize_attacker(), _assert_pending(), _check_and_bump_version(),
  and list_running_topology_deckies() so mypy can see cross-mixin contracts
- Add _require(val, msg) helper for narrowing T | None → T
- Inherit _MixinBase in all 26 leaf mixin classes
- Wrap SQLAlchemy column method calls (.is_(), .like(), .notin_(), .in_(),
  .contains()) with col() from sqlmodel — fixes attr-defined false positives
  caused by pydantic plugin typing class-level fields as Python value types
- Wrap select(Model.field) with select(col(Model.field)) for column projections
- Add pyproject.toml [[tool.mypy.overrides]] to disable arg-type in
  sqlmodel_repo.*: pydantic plugin resolves .where(Model.field == v) as
  where(bool), a false positive; call-arg still catches real argument errors
- Remove 9 stale # type: ignore comments (logging, helpers, credentials)
- Fix telemetry.py traced() overload no-redef + misc
- Fix logs.py datetime/str operator and nullable PK comparison with col()
- sqlmodel_repo/ now has 0 mypy errors

decnet/web/db/sqlmodel_repo/fleet.py

@@ -8,10 +8,13 @@ import orjson
 from sqlalchemy import asc, select, text, update
 
 from decnet.web.db.models import DeckyShard, FleetDecky, LOCAL_HOST_SENTINEL
-from decnet.web.db.sqlmodel_repo._helpers import _deserialize_json_fields
+from decnet.web.db.sqlmodel_repo._helpers import (
+    _MixinBase,
+    _deserialize_json_fields
+)
 
 
-class FleetMixin:
+class FleetMixin(_MixinBase):
     """Mixin: composed onto ``SQLModelRepository``.
 
     ``list_running_deckies`` aggregates topology + fleet + swarm-shard