fix(encyclopedia): tighten assign tests and first-paragraph handling

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Wiki.Application/Encyclopedia/AssignNotesUseCase.cs

@@ -150,7 +150,12 @@ public sealed partial class AssignNotesUseCase(ITextModel model, EncyclopediaSet
             log.LogWarning("Dropping new article {Slug}: empty scope", slug);
             return null;
         }
-        return new PlannedArticle(slug, Text(o["titleDe"]) ?? slug, Text(o["titleEn"]) ?? slug, category, scope, []);
+        if (Text(o["titleDe"]) is not { } titleDe || Text(o["titleEn"]) is not { } titleEn)
+        {
+            log.LogWarning("Dropping new article {Slug}: missing title", slug);
+            return null;
+        }
+        return new PlannedArticle(slug, titleDe, titleEn, category, scope, []);
     }
 
     private static string? Text(JsonNode? n) =>
@@ -177,8 +182,8 @@ public sealed partial class AssignNotesUseCase(ITextModel model, EncyclopediaSet
     private static string FirstParagraph(string body)
     {
         var lines = body.Replace("\r", "").Split('\n')
-            .SkipWhile(l => l.Length == 0 || l.TrimStart().StartsWith('#'))
-            .TakeWhile(l => l.Trim().Length > 0);
+            .SkipWhile(l => string.IsNullOrWhiteSpace(l) || l.TrimStart().StartsWith('#'))
+            .TakeWhile(l => !string.IsNullOrWhiteSpace(l));
         var text = Flatten(string.Join(' ', lines)).Trim();
         return text.Length > FirstParagraphChars ? text[..FirstParagraphChars] : text;
     }

src/Wiki.Application/Encyclopedia/Prompts.cs

@@ -2,7 +2,7 @@ namespace Wiki.Application.Encyclopedia;
 
 /// <summary>
 /// Prompt texts of the encyclopedia. <see cref="Version"/> is bumped by hand whenever a prompt changes,
-/// so that a prompt fix retries earlier rejections and failed plans.
+/// so that a prompt fix retries earlier rejections and failed batches.
 /// </summary>
 public static class Prompts
 {