Add data center demographic, RUCA, and energy capacity analysis

Adds three coordinated changes:

- Request nameplate, summer, and winter capacity from the EIA
  operating-generator-capacity endpoint and project them as typed columns
  on energy_eia_operating_generator_capacity_flat. The original ingest
  only pulled latitude and longitude, leaving the flat table with no MW
  values despite its name.
- New cluster_analysis.ipynb joins master_data_centers to ACS-2024
  demographics, USDA RUCA-2020 codes (loaded from new/), and EIA
  generation capacity within 50 km of each site.
- Summary doc consolidates the headline findings: DC tracts skew higher
  income / more educated / more racially diverse than US average, the
  metro over-index is only 1.11x, the non-metro tail is dominated by
  hyperscalers in the Columbia River corridor (OR+WA = 66% of non-metro
  DCs), and Microsoft co-locates with Palo Verde Nuclear in Goodyear AZ.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ingest_eia_energy_layers.py

@@ -78,7 +78,13 @@ EIA_DATASETS = {
 # values must be requested explicitly. seds returns only id columns; the numeric
 # value column must be requested explicitly.
 EIA_DATASET_DATA_FIELDS = {
-    "electricity/operating-generator-capacity": ["latitude", "longitude"],
+    "electricity/operating-generator-capacity": [
+        "latitude",
+        "longitude",
+        "nameplate-capacity-mw",
+        "net-summer-capacity-mw",
+        "net-winter-capacity-mw",
+    ],
     "electricity/facility-fuel": ["generation", "gross-generation"],
     "seds": ["value"],
 }
@@ -897,6 +903,9 @@ def build_flat_tables(conn):
                         properties->>'balancing-authority-name' as balancing_authority_name,
                         latitude_raw as latitude,
                         longitude_fixed as longitude,
+                        nullif(properties->>'nameplate-capacity-mw', '')::double precision as nameplate_capacity_mw,
+                        nullif(properties->>'net-summer-capacity-mw', '')::double precision as net_summer_capacity_mw,
+                        nullif(properties->>'net-winter-capacity-mw', '')::double precision as net_winter_capacity_mw,
                         properties as raw_properties
                     from fixed
                     """