fix(extension): diff_review steps=[] race condition — in-memory metadata cache (v0.3.13)

Root cause: Collector deletes pending file before Extension reads edit_step_indices.
Fix: diffReviewMetadata Map caches step indices in Extension memory.
Known issue added. Devlog entry 003.

tests/test_diff_review.py

@@ -0,0 +1,25 @@
+"""
+diff_review E2E 테스트용 임시 파일
+생성: 2026-03-16 14:44
+"""
+
+
+def hello(name: str = "World"):
+    """인사 메시지를 반환합니다."""
+    return f"Hello, {name}!"
+
+
+def add(a: int, b: int) -> int:
+    """두 숫자를 더합니다."""
+    return a + b
+
+
+def multiply(a: int, b: int) -> int:
+    """두 숫자를 곱합니다."""
+    return a * b
+
+
+if __name__ == "__main__":
+    print(hello("User"))
+    print(add(1, 2))
+    print(multiply(3, 4))