fix: standardize AppInsights on APPLICATIONINSIGHTS_CONNECTION_STRING

Root cause: workflow was setting ApplicationInsights__ConnectionString (double-underscore
hierarchical .NET config key) which does NOT match the flat env var that UseAzureMonitor()
and Aspire's AzureApplicationInsightsResource both expect.

- workflow: rename ApplicationInsights__ConnectionString -> APPLICATIONINSIGHTS_CONNECTION_STRING
  (both Staging and Production deploy steps; secret reference unchanged)
- Program.cs: remove 3-key fallback chain; single builder.Configuration["APPLICATIONINSIGHTS_CONNECTION_STRING"]
  check; simplify UseAzureMonitor() to no-arg form (auto-reads the canonical env var)

Official docs: 'The Azure Monitor distro expects the environment variable to be
APPLICATIONINSIGHTS_CONNECTION_STRING' (learn.microsoft.com/dotnet/aspire)

Author: BenjaminMichaelis

.github/workflows/Build-Test-And-Deploy.yml

@@ -166,7 +166,7 @@ jobs:
             az containerapp update --name $CONTAINER_APP_NAME --resource-group $RESOURCEGROUP --replace-env-vars Authentication__github__clientId=secretref:github-clientid Authentication__github__clientSecret=secretref:github-clientsecret \
               Authentication__microsoft__clientId=secretref:msft-clientid Authentication__microsoft__clientSecret=secretref:msft-clientsecret AuthMessageSender__ApiKey=secretref:emailsender-apikey AuthMessageSender__SecretKey=secretref:emailsender-secret \
               AuthMessageSender__SendFromName=secretref:emailsender-name AuthMessageSender__SendFromEmail=secretref:emailsender-email ConnectionStrings__EssentialCSharpWebContextConnection=secretref:connectionstring ASPNETCORE_ENVIRONMENT=Staging \
-              AZURE_CLIENT_ID=$AZURECLIENTID HCaptcha__SiteKey=secretref:captcha-sitekey HCaptcha__SecretKey=secretref:captcha-secretkey ApplicationInsights__ConnectionString=secretref:appinsights-connectionstring \
+              AZURE_CLIENT_ID=$AZURECLIENTID HCaptcha__SiteKey=secretref:captcha-sitekey HCaptcha__SecretKey=secretref:captcha-secretkey APPLICATIONINSIGHTS_CONNECTION_STRING=secretref:appinsights-connectionstring \
               AIOptions__Endpoint=secretref:ai-endpoint AIOptions__ApiKey=secretref:ai-apikey AIOptions__VectorGenerationDeploymentName=secretref:ai-vectordeployment AIOptions__ChatDeploymentName=secretref:ai-chatdeployment \
               AIOptions__SystemPrompt=secretref:ai-systemprompt ConnectionStrings__PostgresVectorStore=secretref:postgres-vectorstore-connectionstring \
               TryDotNet__Origin=$TRYDOTNET_ORIGIN
@@ -263,7 +263,7 @@ jobs:
             az containerapp update --name $CONTAINER_APP_NAME --resource-group $RESOURCEGROUP --replace-env-vars Authentication__github__clientId=secretref:github-clientid Authentication__github__clientSecret=secretref:github-clientsecret \
               Authentication__microsoft__clientId=secretref:msft-clientid Authentication__microsoft__clientSecret=secretref:msft-clientsecret AuthMessageSender__ApiKey=secretref:emailsender-apikey AuthMessageSender__SecretKey=secretref:emailsender-secret \
               AuthMessageSender__SendFromName=secretref:emailsender-name AuthMessageSender__SendFromEmail=secretref:emailsender-email ConnectionStrings__EssentialCSharpWebContextConnection=secretref:connectionstring ASPNETCORE_ENVIRONMENT=Production \
-              AZURE_CLIENT_ID=$AZURECLIENTID HCaptcha__SiteKey=secretref:captcha-sitekey HCaptcha__SecretKey=secretref:captcha-secretkey ApplicationInsights__ConnectionString=secretref:appinsights-connectionstring \
+              AZURE_CLIENT_ID=$AZURECLIENTID HCaptcha__SiteKey=secretref:captcha-sitekey HCaptcha__SecretKey=secretref:captcha-secretkey APPLICATIONINSIGHTS_CONNECTION_STRING=secretref:appinsights-connectionstring \
               AIOptions__Endpoint=secretref:ai-endpoint AIOptions__ApiKey=secretref:ai-apikey AIOptions__VectorGenerationDeploymentName=secretref:ai-vectordeployment AIOptions__ChatDeploymentName=secretref:ai-chatdeployment \
               AIOptions__SystemPrompt=secretref:ai-systemprompt ConnectionStrings__PostgresVectorStore=secretref:postgres-vectorstore-connectionstring \
               TryDotNet__Origin=$TRYDOTNET_ORIGIN

EssentialCSharp.Web/Program.cs

@@ -38,14 +38,7 @@ private static void Main(string[] args)
         //   Production:  Azure Monitor (Application Insights) via APPLICATIONINSIGHTS_CONNECTION_STRING
         //   Local/Aspire: OTLP to Aspire Dashboard via OTEL_EXPORTER_OTLP_ENDPOINT
         // Never both simultaneously — that would cause duplicate telemetry in App Insights.
-        // Resolve from all config locations:
-        //   1. Standard Azure Monitor flat env var (SDK's own default key)
-        //   2. Double-underscore (hierarchical) format set by the deployment workflow
-        //   3. GetConnectionString fallback
-        string? appInsightsConnectionString =
-            builder.Configuration["APPLICATIONINSIGHTS_CONNECTION_STRING"]
-            ?? builder.Configuration["ApplicationInsights:ConnectionString"]
-            ?? builder.Configuration.GetConnectionString("ApplicationInsights");
+        string? appInsightsConnectionString = builder.Configuration["APPLICATIONINSIGHTS_CONNECTION_STRING"];
         bool useAzureMonitor = !string.IsNullOrWhiteSpace(appInsightsConnectionString);
         bool useOtlp = !string.IsNullOrWhiteSpace(builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]);
 
@@ -88,7 +81,7 @@ private static void Main(string[] args)
             });
 
         if (useAzureMonitor)
-            otel.UseAzureMonitor(options => options.ConnectionString = appInsightsConnectionString);
+            otel.UseAzureMonitor();
         else if (useOtlp)
             otel.UseOtlpExporter();