feat: add flowing templates and PDF import pipeline

LehrerApp.Templating/Model.cs

@@ -35,6 +35,7 @@ public sealed class TemplateManifest
     public string Description { get; set; } = "";
     public PageSizeDefinition PageSize { get; set; } = new(210, 297);
     public string LayoutFile { get; set; } = "layout.tpl";
+    public string? ContinuationLayoutFile { get; set; }
     public string MetadataFile { get; set; } = TemplateMetadataText.FileName;
     [JsonIgnore]
     public Dictionary<string, string> Metadata { get; set; } = new(StringComparer.OrdinalIgnoreCase);
@@ -54,6 +55,9 @@ public sealed record TextElement(int Line, float X, float Y, string Content, str
 public sealed record TextBoxElement(int Line, float X, float Y, float Width, float Height,
     string Content, string? Placeholder, string? Format, IReadOnlyDictionary<string, string> Attributes)
     : TemplateElement(Line, X, Y, Width, Height, Attributes);
+public sealed record FlowBoxElement(int Line, float X, float Y, float Width, float Height,
+    string Content, string? Placeholder, string? Format, IReadOnlyDictionary<string, string> Attributes)
+    : TemplateElement(Line, X, Y, Width, Height, Attributes);
 public sealed record TableElement(int Line, float X, float Y, float Width, float Height,
     string Placeholder, IReadOnlyDictionary<string, string> Attributes)
     : TemplateElement(Line, X, Y, Width, Height, Attributes);
@@ -71,7 +75,8 @@ public sealed record TemplateLayout(float Width, float Height, string Unit,
     IReadOnlyList<TemplateElement> Elements);
 
 public sealed record LoadedTemplate(TemplateManifest Manifest, TemplateLayout Layout,
-    IReadOnlyDictionary<string, byte[]> Assets, string SourceName = "");
+    IReadOnlyDictionary<string, byte[]> Assets, string SourceName = "",
+    TemplateLayout? ContinuationLayout = null);
 
 public enum ValidationSeverity { Warning, Error }
 public sealed record ValidationIssue(ValidationSeverity Severity, string Message, int? Line = null);