[AZ-357] AC-2 follow-up: populated-duplicates migration test

Closes the partial-coverage gap from batch 10. Adds two integration
tests in MigrationTests.cs:

- DedupeSqlCollapsesDuplicatesByLatestUpdatedAt_AZ357_AC2: seeds a
  session-scoped temp table with intentional 4-column duplicates
  (varying updated_at and id), runs the exact dedupe SQL from
  migration 012, asserts only the expected rows survive (newest
  updated_at wins; ties broken by largest id).
- NewUniqueConstraintExistsOnFourColumns_AZ357_AC2: queries
  pg_indexes against the live DB to assert idx_tiles_unique_location
  is a unique 4-column btree and excludes the version column.

Also wires Npgsql 9.0.2 into the integration-tests project, exposes
DB_CONNECTION_STRING + postgres healthcheck dependency to the test
container in docker-compose.tests.yml, and registers the new tests
in both smoke and full suites.

Implementation note: first attempt used CREATE TEMP TABLE
ON COMMIT DROP, which dropped the table immediately because each
Npgsql command runs in its own implicit transaction. Removed
ON COMMIT DROP — session-scoped temps are dropped on connection
close, which is what we want.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker-compose.tests.yml

@@ -17,12 +17,15 @@ services:
     environment:
       - API_URL=http://api:8080
       - INTEGRATION_TESTS_MODE=${INTEGRATION_TESTS_MODE:-full}
+      - DB_CONNECTION_STRING=Host=postgres;Port=5432;Database=satelliteprovider;Username=postgres;Password=postgres
     volumes:
       - ./ready:/app/ready
       - ./tiles:/app/tiles
     depends_on:
       api:
         condition: service_started
+      postgres:
+        condition: service_healthy
     restart: "no"
 
 volumes: