feat: AI assistant chat widget + session categories + anomaly detection
- Migration 0005: sessions.category, manual_entries.category, ai_flags table, assistant_messages table
- AiFlag + AssistantMessage ORM models added to models.py
- src/services/assistant.py: gap detection (>30min gaps, low active/wall ratio, uncategorized sessions, long days), Anthropic tool_use loop with 7 tools (get_daily_summary, get_sessions, get_project_stats, detect_anomalies, create_manual_entry, set_session_category, get_unresolved_flags)
- src/routers/assistant.py: POST /api/assistant/chat (SSE streaming), GET/DELETE /history, GET /flags, POST /flags/scan, PATCH /flags/:id/resolve, PATCH /sessions/:id/category
- APScheduler: hourly anomaly scan for all users, persists AiFlag records
- AssistantWidget.vue: floating bottom-right chat panel, streaming SSE rendering, quick-hint chips, tool activity indicators, red badge for unresolved flags, markdown rendering, clear history
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>