feat: Implement Runtime Facts ingestion service and NDJSON reader

- Added RuntimeFactsNdjsonReader for reading NDJSON formatted runtime facts.
- Introduced IRuntimeFactsIngestionService interface and its implementation.
- Enhanced Program.cs to register new services and endpoints for runtime facts.
- Updated CallgraphIngestionService to include CAS URI in stored artifacts.
- Created RuntimeFactsValidationException for validation errors during ingestion.
- Added tests for RuntimeFactsIngestionService and RuntimeFactsNdjsonReader.
- Implemented SignalsSealedModeMonitor for compliance checks in sealed mode.
- Updated project dependencies for testing utilities.

src/Signals/StellaOps.Signals/Parsing/RuntimeFactsNdjsonReader.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.IO.Compression;
+using System.Text;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using StellaOps.Signals.Models;
+
+namespace StellaOps.Signals.Parsing;
+
+internal static class RuntimeFactsNdjsonReader
+{
+    private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web);
+
+    public static async Task<List<RuntimeFactEvent>> ReadAsync(
+        Stream input,
+        bool gzipEncoded,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(input);
+
+        Stream effectiveStream = input;
+        if (gzipEncoded)
+        {
+            effectiveStream = new GZipStream(input, CompressionMode.Decompress, leaveOpen: true);
+        }
+
+        using var reader = new StreamReader(effectiveStream, Encoding.UTF8, detectEncodingFromByteOrderMarks: true, leaveOpen: !gzipEncoded);
+
+        var events = new List<RuntimeFactEvent>();
+        string? line;
+        while ((line = await reader.ReadLineAsync(cancellationToken).ConfigureAwait(false)) != null)
+        {
+            if (string.IsNullOrWhiteSpace(line))
+            {
+                continue;
+            }
+
+            var evt = JsonSerializer.Deserialize<RuntimeFactEvent>(line, SerializerOptions);
+            if (evt is null || string.IsNullOrWhiteSpace(evt.SymbolId))
+            {
+                continue;
+            }
+
+            events.Add(evt);
+        }
+
+        return events;
+    }
+}