feat: Ingestion Pipeline Stabilization and WASM Service Proxies (#42)

This PR stabilizes the Nexus Ingestion Engine by implementing functional service proxies for the Blazor WASM client and refining the backend infrastructure for real-time progress tracking and database compatibility.

### Key Changes
- **Infrastructure Stabilization**:
  - Implemented production-grade `EbookRepository` with PostgreSQL `EF.Functions.ILike` support.
  - Enforced `IsReadyForReading = false` state for newly added ebooks (resolves #35).
  - Updated `SignalRSyncBroadcaster` to support targeted user messaging and ingestion-specific progress updates (resolves #37).
- **WASM Client Functional Proxies**:
  - Replaced "Throwing" dummy services with `WasmEbookRepository`, `WasmSyncBroadcaster`, `WasmBookStorageService`, and `WasmEmbeddingGenerator`.
  - These services proxy requests to the backend via a new set of Minimal API endpoints in `NexusReader.Web`.
- **Domain Refinement**:
  - Added `IsReadyForReading` flag to the `Ebook` entity to manage background AI processing states.

### Related Issues
- Fixes #35
- Fixes #36
- Fixes #37

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #42
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -7,7 +7,11 @@ using GeminiDotnet;
 using GeminiDotnet.Extensions.AI;
 using NexusReader.Data.Persistence;
 
+using NexusReader.Application.Abstractions.Messaging;
+using NexusReader.Application.Abstractions.Persistence;
 using NexusReader.Application.Abstractions.Services;
+using NexusReader.Infrastructure.Persistence;
+using NexusReader.Infrastructure.RealTime;
 using NexusReader.Infrastructure.Services;
 using NexusReader.Infrastructure.Configuration;
 using Polly;
@@ -27,12 +31,21 @@ public static class DependencyInjection
         if (!string.IsNullOrEmpty(pgConnectionString))
         {
             services.AddDbContextFactory<AppDbContext>(options =>
+                options.UseNpgsql(pgConnectionString, x => x.UseVector()),
+                ServiceLifetime.Scoped);
+
+            // Also register a scoped DbContext for repositories that need it
+            services.AddDbContext<AppDbContext>(options =>
                 options.UseNpgsql(pgConnectionString, x => x.UseVector()));
         }
         else
         {
             var sqliteConnectionString = configuration.GetConnectionString("SqliteConnection") ?? "Data Source=nexus.db";
             services.AddDbContextFactory<AppDbContext>(options =>
+                options.UseSqlite(sqliteConnectionString),
+                ServiceLifetime.Scoped);
+
+            services.AddDbContext<AppDbContext>(options =>
                 options.UseSqlite(sqliteConnectionString));
         }
 
@@ -40,8 +53,6 @@ public static class DependencyInjection
         services.Configure<StripeSettings>(configuration.GetSection(StripeSettings.SectionName));
         var aiSettings = configuration.GetSection(AiSettings.SectionName).Get<AiSettings>() ?? new AiSettings();
 
-        Console.WriteLine($"[Infrastructure] AI Configured: Model={aiSettings.Model}, KeyPresent={!string.IsNullOrWhiteSpace(aiSettings.ApiKey) && aiSettings.ApiKey != "PLACEHOLDER"}");
-
         if (string.IsNullOrWhiteSpace(aiSettings.ApiKey) || aiSettings.ApiKey == "PLACEHOLDER")
         {
             Console.WriteLine("[Infrastructure] WARNING: AI API Key is missing or placeholder!");
@@ -51,7 +62,7 @@ public static class DependencyInjection
         {
             builder.AddRetry(new RetryStrategyOptions
             {
-                ShouldHandle = new PredicateBuilder().Handle<Exception>(ex => 
+                ShouldHandle = new PredicateBuilder().Handle<Exception>(ex =>
                     ex.Message.Contains("429") || ex.Message.Contains("Too Many Requests") || ex.Message.Contains("quota")),
                 BackoffType = DelayBackoffType.Exponential,
                 UseJitter = true,
@@ -60,10 +71,10 @@ public static class DependencyInjection
             });
         });
 
-        services.AddChatClient(new GeminiChatClient(new GeminiClientOptions 
-        { 
-            ApiKey = aiSettings.ApiKey, 
-            ModelId = aiSettings.Model 
+        services.AddChatClient(new GeminiChatClient(new GeminiClientOptions
+        {
+            ApiKey = aiSettings.ApiKey,
+            ModelId = aiSettings.Model
         }));
 
         services.AddEmbeddingGenerator(new GeminiEmbeddingGenerator(new GeminiClientOptions
@@ -72,10 +83,20 @@ public static class DependencyInjection
             ModelId = aiSettings.EmbeddingModel ?? "text-embedding-004"
         }));
 
+        // Application-layer service implementations
         services.AddScoped<IKnowledgeService, KnowledgeService>();
         services.AddTransient<IEpubReader, EpubReaderService>();
         services.AddTransient<IEpubMetadataExtractor, EpubMetadataExtractor>();
-        services.AddSingleton<IBookStorageService, BookStorageService>();
+
+        // Fix #4: Scoped instead of Singleton — BookStorageService uses path resolution
+        // that is environment-specific and incompatible with Singleton lifetime in MAUI.
+        services.AddScoped<IBookStorageService, BookStorageService>();
+
+        // Fix #1: Ebook repository (scoped, matches AppDbContext lifetime)
+        services.AddScoped<IEbookRepository, EbookRepository>();
+
+        // Fix #2: SignalR broadcaster (scoped, wraps IHubContext which is itself a singleton wrapper)
+        services.AddScoped<ISyncBroadcaster, SignalRSyncBroadcaster>();
 
         services.AddAuthorizationCore(options =>
         {
@@ -83,7 +104,6 @@ public static class DependencyInjection
         });
 
         services.AddScoped<IAuthorizationHandler, ProUserHandler>();
-
         services.AddScoped<IInfrastructureMarker, InfrastructureMarker>();
 
         return services;