Complete End-to-End Prediction Backend API

[Siddharthakhandelwal]

The primary value proposition of Protly is predicting structural insights from a sequence. Currently, the backend REST APIs for this do not correctly process the data or return a complete response.
Tasks/Acceptance Criteria:

• Fully implement and successfully run the GET /api/health health-check endpoint.
• Fully implement POST /api/predict logic.
• Standardize the prediction response into a strict JSON contract containing:
  • pdb: The decoded PDB string.
  • plddt: The mean model confidence score.
  • per-residue plddt: The array of per-residue confidence scores.
  • errors: Specific array mapping API or prediction errors.