[Backend] — Prediction Note Length and Sanitization

[Olowodarey]

Problem
predictions accepts a free-text note without length limits or sanitization, risking storage bloat and stored-XSS via API consumers.

Requirements

• Enforce a max length and strip/escape unsafe content on write.
• Return a clear validation error on violation.
• Tests: over-length rejected; unsafe content sanitized.

Acceptance Criteria

• Prediction notes are bounded and safe. Covered by tests.

Files

• backend/src/predictions/predictions.service.ts
• backend/src/predictions/dto
• backend/src/migrations/1775000000000-AddPredictionNoteColumn.ts