Add Hints Module with Penalty Tracking

[Mkalbani]

Description

Build a hints module that delivers contextual, ordered hints to players during an active session. Hints are a paid mechanic — they cost score points — so the module must integrate tightly with both the sessions and scoring modules. Each puzzle should support up to three tiered hints, with each reveal tracked and penalised.

Acceptance Criteria

• A hints module is scaffolded at src/hints/
• Hint entity is linked to a puzzle with fields: id, puzzleId, order (1–3), and content
• POST /hints/reveal accepts sessionId and returns the next unrevealed hint
• Hint reveals are tracked per session and cannot be repeated
• Each reveal triggers a score penalty via the scoring module
• GET /hints/puzzle/:puzzleId is admin-only and returns all hints for a puzzle
• Attempting to reveal hints in a completed or abandoned session returns a 400
• Unit tests cover ordered reveal, repeat prevention, penalty trigger, and invalid session states