feat: Implement Phase 4 dbt model restructuring

Create neighbourhood-centric dbt transformation layer:

Staging (5 models):
- stg_toronto__neighbourhoods - Neighbourhood dimension
- stg_toronto__census - Census demographics
- stg_toronto__crime - Crime statistics
- stg_toronto__amenities - Amenity counts
- stg_cmhc__zone_crosswalk - Zone-to-neighbourhood weights

Intermediate (5 models):
- int_neighbourhood__demographics - Combined census with quintiles
- int_neighbourhood__housing - Housing + affordability indicators
- int_neighbourhood__crime_summary - Aggregated crime with YoY
- int_neighbourhood__amenity_scores - Per-capita amenity metrics
- int_rentals__neighbourhood_allocated - CMHC via area weights

Marts (5 models):
- mart_neighbourhood_overview - Composite livability score
- mart_neighbourhood_housing - Affordability index
- mart_neighbourhood_safety - Crime rates per 100K
- mart_neighbourhood_demographics - Income/age indices
- mart_neighbourhood_amenities - Amenity index

Closes #60, #61, #62, #63

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

dbt/models/marts/mart_neighbourhood_overview.sql

@@ -0,0 +1,110 @@
+-- Mart: Neighbourhood Overview with Composite Livability Score
+-- Dashboard Tab: Overview
+-- Grain: One row per neighbourhood per year
+
+with demographics as (
+    select * from {{ ref('int_neighbourhood__demographics') }}
+),
+
+housing as (
+    select * from {{ ref('int_neighbourhood__housing') }}
+),
+
+crime as (
+    select * from {{ ref('int_neighbourhood__crime_summary') }}
+),
+
+amenities as (
+    select * from {{ ref('int_neighbourhood__amenity_scores') }}
+),
+
+-- Compute percentile ranks for scoring components
+percentiles as (
+    select
+        d.neighbourhood_id,
+        d.neighbourhood_name,
+        d.geometry,
+        d.census_year as year,
+        d.population,
+        d.median_household_income,
+
+        -- Safety score: inverse of crime rate (higher = safer)
+        case
+            when c.crime_rate_per_100k is not null
+            then 100 - percent_rank() over (
+                partition by d.census_year
+                order by c.crime_rate_per_100k
+            ) * 100
+            else null
+        end as safety_score,
+
+        -- Affordability score: inverse of rent-to-income ratio
+        case
+            when h.rent_to_income_pct is not null
+            then 100 - percent_rank() over (
+                partition by d.census_year
+                order by h.rent_to_income_pct
+            ) * 100
+            else null
+        end as affordability_score,
+
+        -- Amenity score: based on amenities per capita
+        case
+            when a.total_amenities_per_1000 is not null
+            then percent_rank() over (
+                partition by d.census_year
+                order by a.total_amenities_per_1000
+            ) * 100
+            else null
+        end as amenity_score,
+
+        -- Raw metrics for reference
+        c.crime_rate_per_100k,
+        h.rent_to_income_pct,
+        h.avg_rent_2bed,
+        a.total_amenities_per_1000
+
+    from demographics d
+    left join housing h
+        on d.neighbourhood_id = h.neighbourhood_id
+        and d.census_year = h.year
+    left join crime c
+        on d.neighbourhood_id = c.neighbourhood_id
+        and d.census_year = c.year
+    left join amenities a
+        on d.neighbourhood_id = a.neighbourhood_id
+        and d.census_year = a.year
+),
+
+final as (
+    select
+        neighbourhood_id,
+        neighbourhood_name,
+        geometry,
+        year,
+        population,
+        median_household_income,
+
+        -- Component scores (0-100)
+        round(safety_score::numeric, 1) as safety_score,
+        round(affordability_score::numeric, 1) as affordability_score,
+        round(amenity_score::numeric, 1) as amenity_score,
+
+        -- Composite livability score: safety (30%), affordability (40%), amenities (30%)
+        round(
+            (coalesce(safety_score, 50) * 0.30 +
+             coalesce(affordability_score, 50) * 0.40 +
+             coalesce(amenity_score, 50) * 0.30)::numeric,
+            1
+        ) as livability_score,
+
+        -- Raw metrics
+        crime_rate_per_100k,
+        rent_to_income_pct,
+        avg_rent_2bed,
+        total_amenities_per_1000
+
+    from percentiles
+)
+
+select * from final