Revert "refactor: clean up legacy code, rename hopper to entity_extractor, and add third-party notices"

This reverts commit 54fcef9887.

Please do not submit unrelated docs and codes in the same commit. I am reverting this commit so that the related files can be submitted in better-organized future commits.

artemis/utils/shell_utils.py

@@ -0,0 +1,35 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import subprocess
+
+
+def run_shell_command_on_host(command: str) -> str:
+    """Helper to run a shell command on the host and return the output."""
+    try:
+        result = subprocess.run(
+            command,
+            stdin=subprocess.DEVNULL,
+            shell=True,
+            check=True,
+            capture_output=True,
+            text=True,
+        )
+        return result.stdout.strip()
+    except subprocess.CalledProcessError as e:
+        # Log the error and stderr for better debugging
+        error_message = (
+            f"Command '{command}' failed with exit code {e.returncode}.\nStderr: {e.stderr.strip()}"
+        )
+        raise RuntimeError(error_message) from e