feat(telemetry): add telemetry client and services for tracking events

- Implemented TelemetryClient to handle event queuing and flushing to the telemetry endpoint.
- Created TtfsTelemetryService for emitting specific telemetry events related to TTFS.
- Added tests for TelemetryClient to ensure event queuing and flushing functionality.
- Introduced models for reachability drift detection, including DriftResult and DriftedSink.
- Developed DriftApiService for interacting with the drift detection API.
- Updated FirstSignalCardComponent to emit telemetry events on signal appearance.
- Enhanced localization support for first signal component with i18n strings.

src/Scanner/StellaOps.Scanner.Worker/Processing/EpssIngestJob.cs

@@ -152,19 +152,23 @@ public sealed class EpssIngestJob : BackgroundService
                 : _onlineSource;
 
             // Retrieve the EPSS file
-            var sourceFile = await source.GetAsync(modelDate, cancellationToken).ConfigureAwait(false);
+            await using var sourceFile = await source.GetAsync(modelDate, cancellationToken).ConfigureAwait(false);
+
+            // Read file content and compute hash
+            var fileContent = await File.ReadAllBytesAsync(sourceFile.LocalPath, cancellationToken).ConfigureAwait(false);
+            var fileSha256 = ComputeSha256(fileContent);
 
             _logger.LogInformation(
                 "Retrieved EPSS file from {SourceUri}, size={Size}",
                 sourceFile.SourceUri,
-                sourceFile.Content.Length);
+                fileContent.Length);
 
             // Begin import run
             var importRun = await _repository.BeginImportAsync(
                 modelDate,
                 sourceFile.SourceUri,
                 _timeProvider.GetUtcNow(),
-                sourceFile.FileSha256,
+                fileSha256,
                 cancellationToken).ConfigureAwait(false);
 
             _logger.LogDebug("Created import run {ImportRunId}", importRun.ImportRunId);
@@ -172,7 +176,7 @@ public sealed class EpssIngestJob : BackgroundService
             try
             {
                 // Parse and write snapshot
-                await using var stream = new MemoryStream(sourceFile.Content);
+                await using var stream = new MemoryStream(fileContent);
                 var session = _parser.ParseGzip(stream);
 
                 var writeResult = await _repository.WriteSnapshotAsync(
@@ -269,4 +273,10 @@ public sealed class EpssIngestJob : BackgroundService
 
         return new DateTimeOffset(scheduledTime, TimeSpan.Zero);
     }
+
+    private static string ComputeSha256(byte[] content)
+    {
+        var hash = System.Security.Cryptography.SHA256.HashData(content);
+        return Convert.ToHexString(hash).ToLowerInvariant();
+    }
 }