[AZ-362] Refactor C09: idempotent POST contract for caller-supplied GUIDs

Both POST /api/satellite/request and POST /api/satellite/route accept
a caller-supplied id (Guid). Before this change, a retried POST with
the same id would either crash with a unique-key violation (regions)
or quietly create a divergent row (routes), neither of which matched
the documented intent of caller-supplied GUIDs.

RegionService.RequestRegionAsync and RouteService.CreateRouteAsync
now check for an existing row by id at the top of the method. If one
is found, the existing resource is returned with HTTP 200 and the
side effects (insert + enqueue + point regeneration + geofence-region
queueing) are all skipped. The Information-level log line on the
idempotent path makes retries observable.

OpenAPI Description metadata documents the contract on both endpoints
so client integrators see it in Swagger.

Coverage:
- 2 new unit tests (one per service) assert that on duplicate id no
  insert / enqueue / point-generation / region-queueing call is made.
- 2 new integration tests (IdempotentPostTests.cs) exercise the
  contract end-to-end via HTTP, asserting both calls return 200 and
  CreatedAt matches within 1ms (PostgreSQL truncates TIMESTAMP to
  microseconds while .NET DateTime keeps 100ns ticks; a real
  re-insertion would shift CreatedAt by milliseconds at minimum).

Note: the check-first pattern leaves a TOCTOU window for concurrent
retries. The repository unique key still surfaces the race as a
PostgresException which AZ-353 maps to a clean error. Acceptable for
realistic sequential-retry patterns; recorded in batch report as a
non-blocking observation.

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

SatelliteProvider.Services.RouteManagement/RouteService.cs

@@ -26,6 +26,18 @@ public class RouteService : IRouteService
 
     public async Task<RouteResponse> CreateRouteAsync(CreateRouteRequest request)
     {
+        // AZ-362: idempotent POST contract. A retried POST with the same caller-supplied
+        // Id returns the existing route instead of re-running point generation and
+        // re-queueing geofence regions.
+        var existing = await GetRouteAsync(request.Id);
+        if (existing != null)
+        {
+            _logger.LogInformation(
+                "Idempotent route POST: id {RouteId} already exists; returning existing resource",
+                request.Id);
+            return existing;
+        }
+
         if (request.Points.Count < 2)
         {
             throw new ArgumentException("Route must have at least 2 points");