feat: port p-rec-annot elevation subsystem

Plant3D2026/P_Rec_Annot/src/PRecAnnot.Plant3D2026/ElevationRuntimeConfiguration.cs

@@ -0,0 +1,15 @@
+using PRecAnnot.Abstractions;
+using PRecAnnot.Core;
+
+namespace PRecAnnot.Plant3D2026;
+
+internal static class ElevationRuntimeConfiguration
+{
+    public static ElevationAssets Read()
+    {
+        var path = Environment.GetEnvironmentVariable("P_REC_ANNOT_LINE_NUMBER_DRAWING_SETTINGS_PATH");
+        if (string.IsNullOrWhiteSpace(path) || !Path.IsPathFullyQualified(path) || path.StartsWith("\\\\", StringComparison.Ordinal) || !File.Exists(path))
+            throw new InvalidOperationException("ELEVATION_CONFIGURATION_REQUIRED:P_REC_ANNOT_LINE_NUMBER_DRAWING_SETTINGS_PATH");
+        return new ElevationSettingsLoader().Load(File.ReadAllText(path));
+    }
+}