fix(context): replace type: ignore with cast() in ACMSPipeline semantic_chunking registration

Use typing.cast(ContextStrategy, _sc_cls()) instead of a # type: ignore[assignment]
comment when registering SemanticChunkingStrategy in ACMSPipeline.__init__.
This eliminates the type suppression comment and makes the structural subtype
relationship explicit to the type checker.

src/cleveragents/application/services/acms_service.py

@@ -26,7 +26,7 @@ import re
 from collections.abc import Sequence
 from dataclasses import dataclass
 from threading import local
-from typing import TYPE_CHECKING, Any, ClassVar, Protocol, runtime_checkable
+from typing import TYPE_CHECKING, Any, ClassVar, Protocol, cast, runtime_checkable
 
 import structlog
 
@@ -785,7 +785,7 @@ class ACMSPipeline:
         # Imported lazily to avoid circular imports.
         if "semantic_chunking" not in self._strategies:
             _sc_cls = _get_semantic_chunking_strategy_class()
-            self._strategies["semantic_chunking"] = _sc_cls()  # type: ignore[assignment]
+            self._strategies["semantic_chunking"] = cast(ContextStrategy, _sc_cls())
         # Register the 6 spec-required built-in strategies via adapters.
         # These strategies implement the domain-model ContextStrategy protocol
         # (strategy_stubs.py) and are wrapped in SpecStrategyAdapter instances