fix: Update notebooks to use public_marts schema

dbt creates mart tables in public_marts schema, not public.
Updated all notebook SQL queries to use the correct schema.

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

notebooks/demographics/age_distribution.ipynb

@@ -45,8 +45,8 @@
     "    population,\n",
     "    income_quintile,\n",
     "    pct_renter_occupied\n",
-    "FROM mart_neighbourhood_demographics\n",
-    "WHERE year = (SELECT MAX(year) FROM mart_neighbourhood_demographics)\n",
+    "FROM public_marts.mart_neighbourhood_demographics\n",
+    "WHERE year = (SELECT MAX(year) FROM public_marts.mart_neighbourhood_demographics)\n",
     "  AND median_age IS NOT NULL\n",
     "ORDER BY median_age DESC\n",
     "\"\"\"\n",