Add Evidence dashboard pages for e-commerce analytics

[kiyeonjeon21]

Priority: P2

stacks/visualization/evidence/pages/ is empty. Create code-first BI dashboard pages.

What to do

• Configure Evidence PostgreSQL connection in sources/
• Create pages/index.md — revenue overview (daily chart, KPIs)
• Create pages/customers.md — top customers table
• Create pages/products.md — product sales breakdown

Acceptance criteria

• Evidence dev server at :3333 renders all 3 pages
• Pages include at least 2 charts and 2 KPI components
• SQL queries reference dbt mart tables