Add Soda Core quality checks for dbt models

[kiyeonjeon21]

Priority: P1

stacks/quality/soda/checks/ is empty. Create Soda check YAML files that validate the dbt mart tables.

What to do

• Create checks/marts.yml with checks for each mart table
• Create checks/staging.yml for staging views
• Configure configuration.yml pointing to shared PostgreSQL
• Document how to run scans

Acceptance criteria

• docker compose exec ds-soda soda scan passes all checks
• At least 10 checks across 4+ tables
• Covers: row_count, no duplicate PKs, not null, numeric ranges