chore: Delete legacy TRREB dbt models

- Delete stg_trreb__purchases.sql and stg_dimensions__trreb_districts.sql
- Delete int_purchases__monthly.sql
- Delete mart_toronto_purchases.sql and mart_toronto_market_summary.sql
- Update _sources.yml to remove fact_purchases and dim_trreb_district
- Update _staging.yml to remove TRREB staging models
- Update _intermediate.yml to remove int_purchases__monthly
- Update _marts.yml to remove purchase-related marts

Closes #48

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dbt/models/intermediate/_intermediate.yml

@@ -1,17 +1,6 @@
 version: 2
 
 models:
-  - name: int_purchases__monthly
-    description: "Purchase data enriched with time and district dimensions"
-    columns:
-      - name: purchase_id
-        tests:
-          - unique
-          - not_null
-      - name: district_code
-        tests:
-          - not_null
-
   - name: int_rentals__annual
     description: "Rental data enriched with time and zone dimensions"
     columns:

dbt/models/intermediate/int_purchases__monthly.sql

@@ -1,62 +0,0 @@
--- Intermediate: Monthly purchase data enriched with dimensions
--- Joins purchases with time and district dimensions for analysis
-
-with purchases as (
-    select * from {{ ref('stg_trreb__purchases') }}
-),
-
-time_dim as (
-    select * from {{ ref('stg_dimensions__time') }}
-),
-
-district_dim as (
-    select * from {{ ref('stg_dimensions__trreb_districts') }}
-),
-
-enriched as (
-    select
-        p.purchase_id,
-
-        -- Time attributes
-        t.date_key,
-        t.full_date,
-        t.year,
-        t.month,
-        t.quarter,
-        t.month_name,
-
-        -- District attributes
-        d.district_key,
-        d.district_code,
-        d.district_name,
-        d.area_type,
-
-        -- Metrics
-        p.sales_count,
-        p.dollar_volume,
-        p.avg_price,
-        p.median_price,
-        p.new_listings,
-        p.active_listings,
-        p.days_on_market,
-        p.sale_to_list_ratio,
-
-        -- Calculated metrics
-        case
-            when p.active_listings > 0
-            then round(p.sales_count::numeric / p.active_listings, 3)
-            else null
-        end as absorption_rate,
-
-        case
-            when p.sales_count > 0
-            then round(p.active_listings::numeric / p.sales_count, 1)
-            else null
-        end as months_of_inventory
-
-    from purchases p
-    inner join time_dim t on p.date_key = t.date_key
-    inner join district_dim d on p.district_key = d.district_key
-)
-
-select * from enriched