[AZ-808] [AZ-811] Strict validation on region POST + lat/lon GET

AZ-808: FluentValidation for POST /api/satellite/request
- RegionRequestValidator: id non-empty, lat/lon/sizeMeters/zoomLevel ranges
- RequestRegionRequest: [JsonRequired] on every property, no implicit defaults
- Wired via .WithValidation<RequestRegionRequest>() in MapPost chain
- Unit + integration tests + curl probe script
- New contract: contracts/api/region-request.md v1.0.0

AZ-811: FluentValidation + envelope filter for GET /api/satellite/tiles/latlon
- GetTileByLatLonQuery: nullable record (double?/int?) so the minimal-API
  binder never short-circuits with BadHttpRequestException before filters
- GetTileByLatLonQueryValidator: Cascade(Stop) + NotNull + InclusiveBetween
  per param; missing surfaces as `\`<name>\` is required.`
- RejectUnknownQueryParamsEndpointFilter: reusable IEndpointFilter that
  rejects any query key outside the allowed set with errors[<key>] map;
  catches legacy `?Latitude=` typos and hostile probes (`?debug=1&admin=1`)
- Handler: [AsParameters] GetTileByLatLonQuery + .Value deref post-validator
- Unit (validator + filter) + integration tests + curl probe script
- New contract: contracts/api/tile-latlon.md v1.0.0

Shared hygiene
- Promote AssertErrorsContainsMention from per-test-file private helpers to
  ProblemDetailsAssertions (closes batch-1 Low-severity DRY warning)
- Sync Swagger param descriptions, README, blackbox/security/perf scripts,
  uuidv5 doc with the new lat/lon/zoom query-param names

Docs
- system-flows.md F1/F2 reference the new contracts + validation layers
- modules/api_program.md adds Api/Validators + Api/DTOs sections
- _autodev_state.md: batch 2 of 4 complete; next batch = AZ-809

All smoke tests green (mode=smoke, exit 0). AZ-808 + AZ-811 transitioned
to In Testing on Jira.

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

SatelliteProvider.IntegrationTests/ProblemDetailsAssertions.cs

@@ -92,6 +92,46 @@ public static class ProblemDetailsAssertions
         }
     }
 
+    // AZ-808 cycle 8: promoted from per-test-file private helpers (was
+    // duplicated in TileInventoryValidationTests + RegionFieldRenameTests +
+    // RegionRequestValidationTests) so every validation test points at one
+    // source of truth for "is this field-name or substring mentioned anywhere
+    // in the errors map?".
+    public static void AssertErrorsContainsMention(JsonElement problem, string expectedMention, string label)
+    {
+        if (!problem.TryGetProperty("errors", out var errorsEl) || errorsEl.ValueKind != JsonValueKind.Object)
+        {
+            throw new Exception($"{label}: expected 'errors' object in ProblemDetails body.");
+        }
+
+        var found = false;
+        foreach (var prop in errorsEl.EnumerateObject())
+        {
+            if (prop.Name.Contains(expectedMention, StringComparison.OrdinalIgnoreCase))
+            {
+                found = true;
+                break;
+            }
+
+            foreach (var msg in prop.Value.EnumerateArray())
+            {
+                if (msg.GetString()?.Contains(expectedMention, StringComparison.OrdinalIgnoreCase) == true)
+                {
+                    found = true;
+                    break;
+                }
+            }
+
+            if (found) break;
+        }
+
+        if (!found)
+        {
+            var paths = string.Join(", ", errorsEl.EnumerateObject().Select(p => p.Name));
+            throw new Exception($"{label}: expected '{expectedMention}' to appear in errors keys or messages. Available paths: {paths}.");
+        }
+    }
+
     private static IEnumerable<string> EnumeratePaths(JsonElement errorsEl)
     {
         foreach (var prop in errorsEl.EnumerateObject())