fix: apply secret redaction to file tool outputs

Terminal output was already redacted via redact_sensitive_text() but
read_file and search_files returned raw content. Now both tools
redact secrets before returning results to the LLM.

Based on PR #372 by @teyrebaz33 (closes #363) — applied manually
due to branch conflicts with the current codebase.

tests/tools/test_file_tools.py

@@ -38,6 +38,7 @@ class TestReadFileHandler:
     def test_returns_file_content(self, mock_get):
         mock_ops = MagicMock()
         result_obj = MagicMock()
+        result_obj.content = "line1\nline2"
         result_obj.to_dict.return_value = {"content": "line1\nline2", "total_lines": 2}
         mock_ops.read_file.return_value = result_obj
         mock_get.return_value = mock_ops
@@ -52,6 +53,7 @@ class TestReadFileHandler:
     def test_custom_offset_and_limit(self, mock_get):
         mock_ops = MagicMock()
         result_obj = MagicMock()
+        result_obj.content = "line10"
         result_obj.to_dict.return_value = {"content": "line10", "total_lines": 50}
         mock_ops.read_file.return_value = result_obj
         mock_get.return_value = mock_ops