feat(evaluation): add Educational Reasoning to EvaluationReport

[RachitSMane]

Summary

This PR introduces a backend-driven Educational Reasoning system for Evaluation Reports.

The reasoning pipeline generates structured educational insights using deterministic logic derived from:

• Student question responses
• Existing evaluation results
• AI evaluation pipeline outputs
• FLN curriculum structure
• Personalized evaluation summaries

The frontend now consumes this structured reasoning directly from the backend instead of relying on duplicated or heuristic logic.

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What changed

Backend

• Added modular Educational Reasoning engine
• Added curriculum loader for FLN Levels Structure
• Added structured EvaluationReasoning model
• Added evidence generation
• Added learning progression generation
• Added curriculum summary generation
• Added confidence calculation
• Added remediation summary generation
• Integrated reasoning into EvaluationReport
• Replaced duplicated concept mastery logic with backend-generated reasoning

Frontend

• Added Educational Reasoning component
• Updated EvaluationReport types
• Render backend reasoning directly
• Removed dependency on heuristic concept mastery

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Architecture improvements

• Backend is now the single source of truth for Educational Reasoning.
• Concept Mastery is derived from graded question evidence instead of level-based heuristics.
• Curriculum information is loaded from the existing FLN Levels Structure rather than duplicated.
• Reasoning modules are separated into focused builders for easier maintenance.

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Verification

Verified:

• npm run build
• npm run lint
• End-to-end diagnostic workflow
• Worksheet workflow
• Educational Reasoning rendering
• Concept Mastery consistency
• Curriculum summaries
• Learning progression
• Confidence generation

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Notes for reviewers

This PR is intentionally backend-driven.

The frontend now consumes the structured EvaluationReasoning payload without implementing additional educational logic.

The implementation preserves backward compatibility because the reasoning field is optional.