Add user_profiles table, store, and background learner worker
that summarizes user communication style, topics, and personality.
- New user_profiles table (user_id PK, guild_id, profile_summary, last_analyzed_at)
- userProfileStore.ts — CRUD (get/update) following channelCultureStore pattern
- userProfileLearner.ts — background worker: queries 100 recent msgs per user,
calls LLM for personality summary, updates every 12h
- Inject <user_profile> XML tag per-message in moderation prompt
- Start worker alongside cultureLearner in aiAnalyzer.ts
- Migration 0008 for user_profiles table
Co-Authored-By: Claude <noreply@anthropic.com>
