feat(rag): 新增 RagStore（SQLite 向量存储 + 余弦检索，线程安全）

tests/test_rag_store.py

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+import math
+from genesis.rag.store import RagStore
+
+
+def _vec(*ones):
+    v = [0.0] * 8
+    for i in ones:
+        v[i] = 1.0
+    n = math.sqrt(sum(x * x for x in v))
+    return [x / n for x in v]
+
+
+def test_search_returns_most_similar_chunk():
+    s = RagStore(":memory:")
+    s.reset_scope("p1")
+    s.add("p1", ["订单模块处理创建", "用户认证登录"], [_vec(0, 1), _vec(4, 5)])
+    res = s.search("p1", _vec(0, 1), k=1)
+    assert res == ["订单模块处理创建"]
+
+
+def test_reset_scope_clears():
+    s = RagStore(":memory:")
+    s.reset_scope("p1")
+    s.add("p1", ["a"], [_vec(0)])
+    s.reset_scope("p1")
+    assert s.search("p1", _vec(0), k=3) == []
+
+
+def test_concurrent_add_and_search_no_crash():
+    import threading
+    s = RagStore(":memory:")
+    s.reset_scope("p1")
+
+    def worker(i):
+        s.add("p1", [f"chunk-{i}"], [_vec(i % 8)])
+
+    threads = [threading.Thread(target=worker, args=(i,)) for i in range(8)]
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+    res = s.search("p1", _vec(0), k=3)
+    assert len(res) <= 3
+    assert all(isinstance(r, str) for r in res)