Fix Serilog email sink: configure in code, not JSON config

Serilog.Settings.Configuration cannot deserialize NetworkCredential or
MailKit's SecureSocketOptions from JSON, causing an InvalidOperationException
in the binder and preventing containers from starting.

Fix: remove Email from the WriteTo JSON array entirely and wire it in code
inside ConfigureJsonSerilog using a dedicated SerilogEmail:* config section.
The sink is skipped when From/To/Host are absent, so local dev is unaffected.

Also renames the docker-compose env vars from the verbose
Serilog__WriteTo__2__Args__* prefix to the clean SerilogEmail__* prefix.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/rag-api/appsettings.json

@@ -2,8 +2,7 @@
   "Serilog": {
     "Using": [
       "Serilog.Sinks.Console",
-      "Serilog.Sinks.File",
-      "Serilog.Sinks.Email"
+      "Serilog.Sinks.File"
     ],
     "MinimumLevel": {
       "Default": "Information",
@@ -30,23 +29,6 @@
           "retainedFileCountLimit": 30,
           "outputTemplate": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {SourceContext}: {Message:lj}{NewLine}{Exception}"
         }
-      },
-      {
-        "Name": "Email",
-        "Args": {
-          "restrictedToMinimumLevel": "Error",
-          "from": "",
-          "to": "",
-          "host": "",
-          "credentials": {
-            "userName": "",
-            "password": ""
-          },
-          "port": 587,
-          "connectionSecurity": "StartTls",
-          "subject": "[myAi] RAG API Error Alert",
-          "body": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {SourceContext}{NewLine}{Message:lj}{NewLine}{Exception}"
-        }
       }
     ],
     "Enrich": [