Improve MolViewer Resilience and Re-initialization

[Siddharthakhandelwal]

The 3Dmol.js integration supports several visual styles (cartoon, stick, sphere, surface) successfully, but lacks proper cleanup, causing bugs on consecutive predictions.
Tasks/Acceptance Criteria:

• Add explicit React cleanup logic (e.g., inside useEffect returns) to correctly re-initialize the 3Dmol.js viewer on repeated sequence tests.
• Add explicit if/else error catching when pdbData is missing or un-parseable to prevent the renderer from crashing.
• Show user feedback directly on the renderer element (e.g., "Empty PDB data" or "Rendering failed") if it cannot successfully paint the model.