Fix path references in scripts after reorganization

Update 8 scripts to use Path(__file__).parent.parent as PROJECT_ROOT
so they resolve data/, output/, and internet_cables/ relative to the
project root rather than the caller's working directory.

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

scripts/analyze_dc_tract_concentration.py

@@ -12,11 +12,13 @@ import math
 import os
 import statistics
 from collections import Counter
+from pathlib import Path
 
 import psycopg2
 
 
-CSV_PATH = "census_tract_acs_2024_selected_states.csv"
+PROJECT_ROOT = Path(__file__).parent.parent
+CSV_PATH = PROJECT_ROOT / "data" / "census_tract_acs_2024_selected_states.csv"
 
 
 def connect():