feat(rag): 新增 ImpactRAG 索引/检索服务（含 index_dir）

tests/test_impact_rag.py

@@ -0,0 +1,35 @@
+from genesis.rag.embeddings import FakeEmbedder
+from genesis.rag.store import RagStore
+from genesis.rag.impact_rag import ImpactRAG
+
+
+def test_retrieve_returns_relevant_chunk():
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        sources = [
+            ("OrderController.java", "public class OrderController { 创建订单 }"),
+            ("UserAuth.java", "public class UserAuth { 用户登录认证 }"),
+        ]
+        rag.index("p1", sources)
+        res = rag.retrieve("p1", "OrderController 的影响范围", k=1)
+        assert res and "OrderController" in res[0]
+    finally:
+        store.close()
+
+
+def test_index_dir_reads_text_files(tmp_path):
+    (tmp_path / "src").mkdir()
+    (tmp_path / "src" / "OrderController.java").write_text(
+        "public class OrderController { 创建订单 }", encoding="utf-8"
+    )
+    (tmp_path / "src" / "binary.bin").write_bytes(b"\x00\x01")
+    store = RagStore(":memory:")
+    try:
+        rag = ImpactRAG(store, FakeEmbedder())
+        n = rag.index_dir("p1", str(tmp_path / "src"))
+        assert n == 1
+        res = rag.retrieve("p1", "OrderController 的影响范围", k=1)
+        assert res and "OrderController" in res[0]
+    finally:
+        store.close()