[Phase 3.3] XP & Level Progression System

[robinson]

Goal

Implement an experience-point (XP) and levelling system that reflects depth of
learning, not just quantity of interactions.

XP Sources (examples)

Action	XP
Complete a Socratic exchange	20
Earn an achievement badge	50
Finish a session > 15 min	30
Correct answer in Assessment mode	10
Ask a follow-up question	5

Scope

• Backend: xp_events table; GET /progress/:userId returns total XP,
  current level, XP to next level.
• Frontend: XP progress bar in sidebar; level-up animation; level badge on
  profile.
• Level thresholds: 0→100 (Level 1), 100→250 (Level 2), 250→500 … (soft cap
  at Level 20 for now).

Acceptance Criteria

• XP events are recorded per action type with timestamp.
• Progress bar fills and triggers level-up animation at threshold.
• XP totals survive app restarts (persisted in SQLite).
• No XP can be farmed by rapid repeated identical actions (rate limit: same
  action type max once per 60s).

References

• docs/UX_REDESIGN_STRATEGY.md — Part 5: Gamification (XP & Level Progression)

Phase

Phase 3 — Gamification & Progress · Week 3–5