Server-side evaluation session tracking

Overview

Track evaluation sessions on the server to maintain a history of user activity. Currently sessions are managed client-side only and are lost when the browser session ends.

Motivation

• Persist session history across browser sessions
• Enable user stats features (#96) that require historical data
• Support future features like session resumption

Feature Description

Backend

• New data model for sessions (user, start time, end time, politicians evaluated)
• API endpoints:
  • POST /sessions - Create a new session when user starts evaluating
  • PATCH /sessions/{id} - Update session (mark complete, update count)
  • GET /sessions - List user's session history

Frontend

• Update EvaluationSessionContext to sync with backend
• Session ID persisted and sent with evaluation submissions

Notes

This is a prerequisite for accurate user stats (#96) - specifically tracking "sessions completed" requires server-side session records.

Supersedes session tracking aspects from #82.

Start by reading the Backend and Frontend sections, then inspect EvaluationSessionContext and the existing evaluation submission flow. Define the session model and the POST, PATCH, and GET /sessions entry points, and verify that session IDs and history synchronize across browser sessions. Done means session records support creation, updates, listing, and frontend syncing.