feat: implement AI-driven knowledge extraction service with semantic caching and persistent storage

src/NexusReader.Application/Abstractions/Services/IKnowledgeService.cs

@@ -0,0 +1,9 @@
+using FluentResults;
+using NexusReader.Application.DTOs.AI;
+
+namespace NexusReader.Application.Abstractions.Services;
+
+public interface IKnowledgeService
+{
+    Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, CancellationToken cancellationToken = default);
+}

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

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+using System.Text.Json.Serialization;
+
+namespace NexusReader.Application.DTOs.AI;
+
+public record KeyConcept(
+    [property: JsonPropertyName("title")] string Title,
+    [property: JsonPropertyName("description")] string Description
+);
+
+public record QuizQuestion(
+    [property: JsonPropertyName("question")] string Question,
+    [property: JsonPropertyName("options")] List<string> Options,
+    [property: JsonPropertyName("correct_index")] int CorrectIndex
+);
+
+public record KnowledgePacket(
+    [property: JsonPropertyName("concepts")] List<KeyConcept> Concepts,
+    [property: JsonPropertyName("quizzes")] List<QuizQuestion> Quizzes
+);