Add SqlExceptionTranslator config and options class

Introduce SqlExceptionTranslator section in appsettings.json to map common SQL error codes to user-friendly messages. Add SqlExceptionTranslatorOptions class to manage error code/message mapping and support configuration binding.

src/ReC.API/appsettings.json

@@ -8,6 +8,14 @@
   "RecAction": {
     "MaxConcurrentInvocations": 5
   },
+  "SqlExceptionTranslator": {
+    "ErrorMessages": {
+      "515": "{Operation} '{Target}' failed because a required field was not provided or was null. Verify mandatory values and retry.",
+      "547": "{Operation} '{Target}' failed because one or more referenced entities do not exist or violate relational rules. Please verify identifiers and constraints.",
+      "2601": "{Operation} '{Target}' failed because the data conflicts with a unique constraint. Remove duplicate values and retry.",
+      "2627": "{Operation} '{Target}' failed because the data conflicts with a unique constraint. Remove duplicate values and retry."
+    }
+  },
   "AddedWho": "ReC.API",
   "FakeProfileId": 2
 }