[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>

SatelliteProvider.IntegrationTests/SatelliteProvider.IntegrationTests.csproj

@@ -7,4 +7,8 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Npgsql" Version="9.0.2" />
+  </ItemGroup>
+
 </Project>