[chore] remove all remaining type:ignore suppressions from tests/

Converts 115 `# type: ignore[...]` suppressions across 23 test files to
no-suppression patterns (helper-return widening to Any, local Any aliases,
cc:Any aliases, cast at narrow call sites, typed fixtures) so the hard
no-type:ignore convention holds across tests/. No test logic or assertions
changed — only mock-wiring mechanics and type annotations.

Gate: ruff check tests/ clean; mypy tests/ (538 files) clean; 176 changed-file
tests pass. Zero real suppressions remain (the 7 grep hits are 3 hygiene-
checker string-literal test inputs and 4 prose mentions in comments).

tests/unit/services/test_conventions_resolve.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 import subprocess
 from types import SimpleNamespace
-from typing import TYPE_CHECKING, cast
+from typing import TYPE_CHECKING, Any, cast
 
 from roboco.services.conventions import ConventionsService
 
@@ -33,7 +33,7 @@ def _git_repo(root: Path) -> str:
 
 
 def _svc() -> ConventionsService:
-    return ConventionsService(session=None)  # type: ignore[arg-type]
+    return ConventionsService(session=cast("Any", None))
 
 
 def test_resolve_reads_clone_head_and_backfills(tmp_path: Path) -> None: