feat: implement semantic search, knowledge unit extraction, and visualization components

src/NexusReader.Application/DTOs/AI/KnowledgePacket.cs

@@ -13,10 +13,15 @@ public record QuizQuestion(
     [property: JsonPropertyName("correct_index")] int CorrectIndex
 );
 
+public record KnowledgeUnitDto(string Id, string Type, string Content, Dictionary<string, object>? Metadata = null);
+public record KnowledgeLinkDto(string Source, string Target, string Relation);
+
 public record KnowledgePacket
 {
     [JsonPropertyName("concepts")] public List<KeyConcept> Concepts { get; init; } = new();
     [JsonPropertyName("quizzes")] public List<QuizQuestion> Quizzes { get; init; } = new();
+    [JsonPropertyName("units")] public List<KnowledgeUnitDto> Units { get; init; } = new();
+    [JsonPropertyName("links")] public List<KnowledgeLinkDto> Links { get; init; } = new();
     [JsonPropertyName("graph")] public NexusReader.Application.Queries.Graph.GraphDataDto? Graph { get; init; }
     [JsonPropertyName("summary")] public string? Summary { get; init; }
 }

src/NexusReader.Application/DTOs/AI/RelevantContext.cs

@@ -0,0 +1,8 @@
+namespace NexusReader.Application.DTOs.AI;
+
+public class RelevantContext
+{
+    public string Text { get; set; } = string.Empty;
+    public string SourceId { get; set; } = string.Empty; // ContentHash or EbookTitle
+    public double Confidence { get; set; }
+}

src/NexusReader.Application/DTOs/AI/SemanticSearchResultDto.cs

@@ -0,0 +1,11 @@
+namespace NexusReader.Application.DTOs.AI;
+
+public class SemanticSearchResultDto
+{
+    public string ContentHash { get; set; } = string.Empty;
+    public string Snippet { get; set; } = string.Empty;
+    public string? UnitType { get; set; }
+    public float RelevanceScore { get; set; }
+    public string? SourceBookTitle { get; set; }
+    public Dictionary<string, object>? Metadata { get; set; } // Bonus context
+}