Api Learning Remediation Pending

Return the user's pending remediation events ripe for re-check.

Phase 5 of the Adaptive Mastery System. Feeds the morning-brief panel's 'Lock in X from N days ago' prompt. Unauthenticated users get an empty list (no events to track); the frontend can skip rendering when the response is empty.

Filter (mirrors list_pending_rechecks):

• user_id matches session
• reattempt_at IS NULL (the loop is still open)
• remediation_shown_at between 48h and 30 days ago (ripe but not stale)

One row per module_id (the most recent pending event for that module), capped at 3 so the morning brief doesn't overflow. Each row carries: event_id, module_id, module_title (resolved server-side from learning-paths.json), mastery_score, shown_at_relative (human-readable).