Add standardized sentiment output schema for usability reports

[SuryaRNaik]

This PR introduces a standardized JSON schema for sentiment, emotion,
and intent outputs used in usability evaluation reports.

Key features:

• Defines sentiment categories (positive, negative, neutral)
• Includes emotion classification examples
• Provides intent classification
• Adds confidence scoring structure
• Supports human-readable explanation output

This schema will help ensure consistent sentiment output formatting
across RUXAILAB analysis pipelines and reporting tools.