Store Routing - TraceLM

Controls stage rollout (postgres, canary, partial, columnar_primary) and shadow-write behavior.

{
  "project_id": "550e8400-e29b-41d4-a716-446655440000",
  "read_mode": "postgres",
  "write_mode": "postgres_primary",
  "selected_store": "pinot",
  "canary_read_percent": 5,
  "partial_read_percent": 25,
  "shadow_writes_enabled": true,
  "notes": "Stage 1 shadow writes"
}