chore(types): annotate fifteen signatures mypy could not check

Twelve gain `-> None`, each confirmed by AST to contain no returning
`return` and no `yield` rather than by reading the name and assuming.
The three context-manager exits gain the canonical
type[BaseException]/BaseException/TracebackType argument triple.

Both files taking TracebackType needed the import, and inserting it
before the first import broke ruff's I001 — lint was exit 0 at the
baseline commit, verified by stashing this work and re-running, so that
breakage was mine. Fixed with `ruff check --fix` on the two files, which
placed the import in sorted position.

86 errors -> 75; no-untyped-def 29 -> 14.

Suite: 658 passed. The baseline was 657 passed with one failure in
test_tatlock_tool_call_logging_calculator, which asserts on the content
of a live model's reply. It passing here is nondeterminism, NOT evidence
this commit fixed anything, and it may fail again on the next run.

Co-Authored-By: Claude <noreply@anthropic.com>

src/agents/delegation.py

@@ -218,7 +218,7 @@ class DelegationTask:
     result: str | None = None
     task_id: str = ""
 
-    def __post_init__(self):
+    def __post_init__(self) -> None:
         """Generate task ID if not provided."""
         if not self.task_id:
             import uuid