feat(marts): add fact_payments model (Phase 2.2)

dbt/models/marts/facts/_fact_payments.yml

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+version: 2
+
+models:
+  - name: fact_payments
+    description: >
+      Payments fact table.
+      Grain: 1 row per payment_key (surrogate key of order_id + payment_sequential).
+      order_purchase_date is sourced via LEFT JOIN with int_orders_enriched on order_id.
+      Tradeoff: using int_orders_enriched avoids a mart-to-mart dependency
+      that would arise from joining fact_orders directly.
+    config:
+      tags: ['marts', 'fact', 'payments']
+    columns:
+      - name: payment_key
+        description: Surrogate key — grain of this model (order_id + payment_sequential)
+        tests:
+          - not_null
+          - unique
+
+      - name: order_id
+        description: FK to orders
+        tests:
+          - not_null
+          - relationships:
+              to: ref('int_orders_enriched')
+              field: order_id
+              config:
+                severity: warn
+
+      - name: payment_sequential
+        description: Payment sequence number within the order
+        tests:
+          - not_null
+
+      - name: payment_type
+        description: Raw payment method
+        tests:
+          - not_null
+
+      - name: payment_type_clean
+        description: Cleaned payment method (lowercase, trimmed)
+
+      - name: payment_installments
+        description: Number of installments
+        tests:
+          - not_null
+
+      - name: payment_value
+        description: Payment amount in BRL
+        tests:
+          - not_null
+
+      - name: order_purchase_date
+        description: >
+          Purchase date from int_orders_enriched via LEFT JOIN on order_id.
+          Can be null if the order has no matching record in the intermediate layer.
+
+      - name: is_negative_value
+        description: Flag for payments with value < 0
+
+      - name: is_invalid_installments
+        description: Flag for installments < 1
+
+      - name: is_excessive_installments
+        description: Flag for card payments with installments > 24

dbt/models/marts/facts/fact_payments.sql

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+{{
+    config(
+        materialized='table',
+        tags=['marts', 'fact', 'payments']
+    )
+}}
+
+with payments as (
+    select * from {{ ref('stg_payments') }}
+),
+
+orders as (
+    select
+        order_id,
+        cast(purchased_at as date) as order_purchase_date
+    from {{ ref('int_orders_enriched') }}
+),
+
+final as (
+    select
+        p.payment_key,
+        p.order_id,
+        p.payment_sequential,
+        p.payment_type,
+        p.payment_type_clean,
+        p.payment_installments,
+        p.payment_value,
+        p.is_negative_value,
+        p.is_invalid_installments,
+        p.is_excessive_installments,
+        o.order_purchase_date
+    from payments p
+    left join orders o
+        on p.order_id = o.order_id
+)
+
+select * from final