fix: remove hardcoded internal OTLP endpoint from default config

The Telemetry:Otlp:Endpoint was set to the internal collector URL,
causing all user deployments to silently send telemetry to our server.

Default is now empty string (no export). Users opt-in by setting
Telemetry__Otlp__Endpoint via appsettings.json or environment variable.

Author: mrdevrobot

AGENTS.md

@@ -393,7 +393,7 @@ Do **not** add comments that paraphrase the code. Only add comments that explain
     "Enabled": true,
     "ServiceName": "blite-server",
     "Console": null,
-    "Otlp": { "Endpoint": "https://..." }
+    "Otlp": { "Endpoint": "" }           // empty = disabled; set to your collector URL to enable
   },
   "License": {
     "SourceUrl": "https://github.com/EntglDb/BLite.Server"

src/BLite.Server/appsettings.json

@@ -55,7 +55,7 @@
     "ServiceName": "blite-server",
     "Console": null,
     "Otlp": {
-      "Endpoint": "https://otel.blitedb.com"
+      "Endpoint": ""
     }
   },
   "Transactions": {