Add LegiScan legislation ingestion and analysis queries

Adds ingest_legiscan.py to pull all US state + federal bills (2016-2026)
from the LegiScan API into legiscan_sessions and legiscan_bills tables.
Bills are keyword-tagged across 8 research categories (data_center,
ratepayer_protection, large_load, grid_impact, tax_incentive, etc.).
Loads ~1.3M bills; ~60K tagged relevant. Adds query_legiscan_bills.sql
with pre-built analysis queries including state/DC joins. Updates
database-tables.md, README.md, and research-ideas.md accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -87,6 +87,7 @@ Facilities in DBSCAN clusters differ significantly from isolated sites:
 - **NOAA HMS Smoke Data**: Wildfire smoke exposure (2005-2025)
 - **USDM Drought Data**: Drought severity
 - **Utility Rate Tracker**: State-level electricity rate increases
+- **LegiScan Legislative Data**: All US state + federal bills 2016–2026 (1.3M bills, 646 sessions), tagged for data center, ratepayer, grid, tax, and siting topics
 
 ## Repository Structure
 
@@ -99,6 +100,7 @@ Facilities in DBSCAN clusters differ significantly from isolated sites:
 - `load_postgis_internet_cables.py` - Load submarine cables and landing points
 - `ingest_eia_energy_layers.py` - Ingest EIA energy data via API
 - `build_watershed_huc8_tables.py` - Load USGS HUC8 watersheds
+- `ingest_legiscan.py` - Download all US state/federal bills 2016–2026 via LegiScan API, tag for data center research topics
 
 **Enrichment**
 - `create_data_center_census_tract_table.py` - Join data centers to Census tracts with ACS demographics
@@ -151,6 +153,7 @@ Credentials stored in `~/.zsh_secrets`, loaded via environment variables:
 - `FCC_USERNAME`, `FCC_API_KEY`: FCC broadband data
 - `RDH_USERNAME`, `RDH_PASSWORD`: Redistricting Data Hub
 - `CENSUS_API_KEY`: Census ACS API
+- `LEGISCAN_API_KEY`: LegiScan legislative data
 
 ## Quick Start
 
@@ -174,6 +177,11 @@ python3 analyze_cables_concentration.py > output/cables_analysis.txt
 
 # 4. Execute notebooks
 jupyter notebook cluster_analysis.ipynb
+
+# 5. Load legislation (all states, 2016-2026)
+python3 ingest_legiscan.py --all
+# Weekly refresh (skips unchanged sessions):
+python3 ingest_legiscan.py --fetch --load
 ```
 
 ### Generate Maps