Split subject-level data list in API response into imaging and phenotypic session arrays

Current response:

[
  {
    "dataset_uuid": "http://neurobagel.org/vocab/e0c7d08c-edcc-4c2a-816a-306878ed7be2",
    "dataset_name": "BIDS synthetic",
    "dataset_portal_uri": "https://github.com/bids-standard/bids-examples",
    "dataset_total_subjects": 5,
    "records_protected": false,
    "num_matching_subjects": 5,
    "subject_data": [
      {
        "sub_id": "sub-01",
        "session_id": "ses-01",
        "num_phenotypic_sessions": 2,
        "num_imaging_sessions": 2,
        "session_type": "http://neurobagel.org/vocab/ImagingSession",
        "age": null,
        "sex": null,
        "diagnosis": [
          null
        ],
        "subject_group": null,
        "assessment": [
          null
        ],
        "image_modal": [
          "http://purl.org/nidash/nidm#T1Weighted",
          "http://purl.org/nidash/nidm#FlowWeighted"
        ],
        "session_file_path": "/data/neurobagel/bagel-cli/bids-examples/synthetic/sub-01/ses-01"
      },
      {
        "sub_id": "sub-01",
        "session_id": "ses-01",
        "num_phenotypic_sessions": 2,
        "num_imaging_sessions": 2,
        "session_type": "http://neurobagel.org/vocab/PhenotypicSession",
        "age": 34.1,
        "sex": "http://purl.bioontology.org/ontology/SNOMEDCT/248152002",
        "diagnosis": [
          null
        ],
        "subject_group": "http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl#C94342",
        "assessment": [
          "https://www.cognitiveatlas.org/task/id/trm_57964b8a66aed",
          "https://www.cognitiveatlas.org/task/id/tsk_4a57abb949ece"
        ],
        "image_modal": [
          null
        ],
        "session_file_path": null
      },

Motivations for keeping this response:

No source file, test, or entry point is named in the issue. Start by locating the API response assembly that produces subject_data, then confirm the response separates imaging and phenotypic sessions into distinct arrays and add or update coverage for the revised shape.