chore: initialize insar management system v2

backend/migrations/001_st_intersection_agg.sql

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+-- Migration: Create st_intersection_agg function for efficient geometry intersection
+-- This function reduces a set of geometries to their geometric intersection.
+-- If no geometries are provided, it returns NULL.
+
+-- Drop existing aggregate and function if they exist (for idempotency)
+DROP AGGREGATE IF EXISTS st_intersection_agg(geometry);
+DROP FUNCTION IF EXISTS st_intersection_agg(geometry, geometry);
+
+-- Create the aggregation function
+CREATE OR REPLACE FUNCTION st_intersection_agg(g1 geometry, g2 geometry)
+RETURNS geometry AS
+$$
+    SELECT CASE WHEN g1 IS NULL THEN g2
+                WHEN g2 IS NULL THEN g1
+                ELSE ST_Intersection(g1, g2) END;
+$$
+LANGUAGE SQL;
+
+COMMENT ON FUNCTION st_intersection_agg(geometry, geometry) IS
+'Aggregates a set of geometries by computing the intersection pairwise. Returns NULL if input is empty.';
+
+-- Create aggregate wrapper for single-argument usage in SQL queries
+CREATE AGGREGATE st_intersection_agg(geometry) (
+    SFUNC = st_intersection_agg,
+    STYPE = geometry
+);
+
+COMMENT ON AGGREGATE st_intersection_agg(geometry) IS
+'Aggregates a set of geometries by computing the intersection pairwise.';