Fix SQL injection in the /query/city aggregation route

field on that route reached PostgresService.query unvalidated, which splices
it into SQL via Fragment.const (unescaped) whenever the aggregate key is
min/max/avg/sum/distinct, or whenever granularity is "hour" in the list
branch. Add ValidateField (allowlists WeatherData's known field names, same
pattern AggFieldList already uses for /query/country) and apply it to the
field path segment. AggregateKey values reaching Fragment.const elsewhere are
already safe since they come from a closed ADT, not raw user input.

src/main/scala/server/Server.scala

@@ -10,7 +10,7 @@ import fetch.csv.FileNameService
 import fetch.lvgmc.{FetchService, WaterTemperatureService}
 import fetch.warnings.WarningService
 import fs2.io.file.{Files, Path}
-import server.ValidateRoutes.{AggFieldList, AggKey, CityList, DateTimeRange, Granularity, ValidateDate, ValidateDateTime, ValidateFileName, ValidateInt, ValidateMonths, ValidateZonedDateTime}
+import server.ValidateRoutes.{AggFieldList, AggKey, CityList, DateTimeRange, Granularity, ValidateDate, ValidateDateTime, ValidateField, ValidateFileName, ValidateInt, ValidateMonths, ValidateZonedDateTime}
 import org.http4s._
 import org.http4s.dsl.io._
 import org.http4s.implicits._
@@ -139,7 +139,7 @@ class Server(postgresService: PostgresService, dataService: DataService, fetch:
       }
 
     // http://0.0.0.0:8080/api/query/city/Liepāja,Rēzekne/20230414_2200-20230501_1230/hour/tempMax/max
-    case GET -> Root / "query" / "city" / CityList(cities) / DateTimeRange(from, to) / Granularity(granularity) / field / AggKey(key) =>
+    case GET -> Root / "query" / "city" / CityList(cities) / DateTimeRange(from, to) / Granularity(granularity) / ValidateField(field) / AggKey(key) =>
       val userQuery = UserQuery(cities, field, key, granularity, from, to)
 
       postgresService.query(userQuery)

src/main/scala/server/ValidateRoutes.scala

@@ -64,6 +64,14 @@ object ValidateRoutes {
     }
   }
 
+  // Restricts a raw path segment to a known WeatherData field name before it
+  // can reach Fragment.const (unescaped SQL splicing) in PostgresService.
+  object ValidateField {
+    def unapply(str: String): Option[String] = {
+      if (WeatherData.getKeys.contains(str)) Some(str) else None
+    }
+  }
+
   object AggFieldList {
     def unapply(str: String): Option[NonEmptyList[String]] = {
       val weatherFields = WeatherData.getKeys