Add sample data generator with 9 e-commerce tables
Synthetic data generator for demo/testing without real data adapter:
- 9 tables: customers, products, campaigns, web_sessions, web_leads,
orders, order_items, payments, support_tickets
- 4 size presets: xs (1MB), s (15MB), m (150MB), l (1.5GB)
- Realistic patterns: seasonality, Pareto customer distribution,
segment-based behavior, referential integrity
- Deterministic output via --seed parameter
Also: docs/sample-data.md, updated auto-install.md with Step 6,
updated CLAUDE.md (email auth provider, dual-repo architecture)
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