Add asset metadata, sharing, and MinIO-backed signed links.

This introduces deduplicated per-user image/3D asset records linked into feature properties, adds visibility-controlled download routing, and wires local S3-compatible storage with automatic bucket bootstrap in Docker Compose.

Made-with: Cursor

internal/store/migrations/0003_features_spatial.sql

@@ -0,0 +1,21 @@
+CREATE EXTENSION IF NOT EXISTS postgis;
+
+ALTER TABLE features
+  ADD COLUMN IF NOT EXISTS geom geometry(PointZ, 4326);
+
+UPDATE features
+SET geom = ST_SetSRID(
+  ST_MakePoint(
+    (geometry->'coordinates'->>0)::double precision,
+    (geometry->'coordinates'->>1)::double precision,
+    CASE
+      WHEN jsonb_array_length(geometry->'coordinates') >= 3 THEN (geometry->'coordinates'->>2)::double precision
+      ELSE 0
+    END
+  ),
+  4326
+)
+WHERE geom IS NULL
+  AND geometry ? 'coordinates';
+
+CREATE INDEX IF NOT EXISTS idx_features_geom_gist ON features USING GIST (geom);