feat(tree-sitter-overlay-extra): parse JS/C/Java overlay via optional extra

Add openultrasast[semantic] with official grammar wheels and one CST walker
into FileIR. quick stays extra-free. Host CLI is not overlay-ready. Default CI
stays extra-free; a semantic job runs pytest -m semantic.

src/openultrasast/semantic/__init__.py

@@ -1,6 +1,7 @@
 """Propose/adjudicate/prove overlay: regex proposes, semantics adjudicates."""
 
 from .engines import joern_available, tree_sitter_available
+from .extra import grammar_for, has_semantic_extra
 from .facts import FactLoadError, SemanticFacts, load_facts
 from .mechanisms import Mechanism, MechanismStore, append_mechanism, order_promotions
 from .overlay import OverlayError, OverlayRecord, adjudicate, finding_from_coverage, write_overlay
@@ -17,6 +18,8 @@ __all__ = [
     "append_mechanism",
     "filter_promoted_hotspots",
     "finding_from_coverage",
+    "grammar_for",
+    "has_semantic_extra",
     "joern_available",
     "load_facts",
     "order_promotions",