[fix] MegaTask verification: migration 052 enum + async cell-map read

Two real bugs surfaced running the full gate against a containerized
Postgres (and the orchestrator boot log):

1. Migration 052 crashed a real orchestrator boot with
   'type "team" already exists'. The generic sa.Enum(create_type=False)
   does NOT set the postgres enum's create_type attribute, so op.create_table
   (checkfirst=False) emitted a redundant CREATE TYPE against the pre-existing
   team enum. Switched to postgresql.ENUM(create_type=False) — the postgres-
   native enum whose create_type _check_for_name_in_memos actually reads, so
   the CREATE TYPE is suppressed. Verified: 051->052 upgrade against a DB where
   the team enum pre-existed (the exact path that crashed) now succeeds;
   downgrade 052->051 drops the table and preserves the shared enum; fresh
   upgrade head clean. (Migration 016 has the same latent sa.Enum pattern but
   never re-runs in prod, so it's noted, not touched here.)

2. _ensure_branch_for_task read task.cell_projects (lazy=selectin to-many)
   directly, tripping MissingGreenlet on a freshly-created/unqueried task —
   which then poisoned the async session (PendingRollbackError). Replaced with
   _task_has_cell_map: peeks InstanceState.unloaded (no IO) and reads the
   already-loaded map, falling back to an awaited count query only when the
   relationship is genuinely unloaded. Non-ORM stubs route to the plain
   attribute. Fixes 2 integration tests; the 6 cell-map unit tests still pass.

Also: typed the self stub as Any in test_choreographer_subtask_project
(mypy tests/ wants Choreographer, not SimpleNamespace) — the codebase idiom.

Gate: ruff format/check clean; mypy roboco/ + tests/ clean; full pytest
10371 passed / 388 skipped against containerized pgvector:pg16; vulture clean.
Pre-existing xenon C-rank on reassign (from prior commit 19a474d3, not this
feature) still blocks make quality — surfaced separately.

tests/unit/services/test_choreographer_subtask_project.py

@@ -17,6 +17,7 @@ other tiers are unchanged product-root / single-project behavior.
 from __future__ import annotations
 
 from types import SimpleNamespace
+from typing import Any
 from uuid import UUID, uuid4
 
 import pytest
@@ -54,7 +55,7 @@ async def test_explicit_inputs_project_id_wins_over_cell_map() -> None:
         product_id=None,
         project_id=None,
     )
-    self_stub = SimpleNamespace(product=None)
+    self_stub: Any = SimpleNamespace(product=None)
     resolved = await Choreographer._resolve_subtask_project(
         self_stub, parent, _inputs(team=Team.BACKEND, project_id=explicit)
     )
@@ -73,7 +74,7 @@ async def test_cell_map_resolves_project_for_matching_team() -> None:
         product_id=None,
         project_id=None,
     )
-    self_stub = SimpleNamespace(product=None)
+    self_stub: Any = SimpleNamespace(product=None)
     resolved = await Choreographer._resolve_subtask_project(
         self_stub, parent, _inputs(team=Team.BACKEND)
     )
@@ -90,7 +91,7 @@ async def test_cell_map_missing_team_falls_through_to_parent_project() -> None:
         product_id=None,
         project_id=own,
     )
-    self_stub = SimpleNamespace(product=None)
+    self_stub: Any = SimpleNamespace(product=None)
     # Frontend subtask but the map only covers backend → fall to parent.project_id.
     resolved = await Choreographer._resolve_subtask_project(
         self_stub, parent, _inputs(team=Team.FRONTEND)
@@ -109,7 +110,7 @@ async def test_cell_map_only_parent_with_no_match_raises_completeness() -> None:
         product_id=None,
         project_id=None,
     )
-    self_stub = SimpleNamespace(product=None)
+    self_stub: Any = SimpleNamespace(product=None)
     with pytest.raises(TaskCompletenessError) as exc:
         await Choreographer._resolve_subtask_project(
             self_stub, parent, _inputs(team=Team.FRONTEND)