Add genre feature; extract ConfirmModal for reusable confirm dialogs

Genres seed on boot, are editable per project, and gate agent config
errors more gracefully. ConfirmModal replaces ad-hoc confirm prompts
across chapters, tags, and characters pages.

src/Novelly.Api/Data/NovelDbContext.cs

@@ -4,6 +4,7 @@ using Novelly.Api.Agent;
 using Novelly.Api.Beats;
 using Novelly.Api.Chapters;
 using Novelly.Api.Characters;
+using Novelly.Api.Genres;
 using Novelly.Api.Imports;
 using Novelly.Api.Projects;
 using Novelly.Api.Questions;
@@ -30,6 +31,7 @@ public class NovelDbContext(DbContextOptions<NovelDbContext> options)
     public DbSet<AgentConversation> Conversations => Set<AgentConversation>();
     public DbSet<AgentMessage> AgentMessages => Set<AgentMessage>();
     public DbSet<ImportJob> ImportJobs => Set<ImportJob>();
+    public DbSet<Genre> Genres => Set<Genre>();
 
     Task<int> INovelDbContext.SaveChangesAsync(CancellationToken cancellationToken) =>
         base.SaveChangesAsync(cancellationToken);
@@ -150,6 +152,13 @@ public class NovelDbContext(DbContextOptions<NovelDbContext> options)
             entity.HasIndex(m => new { m.ConversationId, m.Sequence }).IsUnique();
         });
 
+        builder.Entity<Genre>(entity =>
+        {
+            entity.Property(g => g.Name).IsRequired().HasMaxLength(100);
+            entity.HasIndex(g => g.Name).IsUnique();
+            entity.HasData(SeededGenres.All);
+        });
+
         builder.Entity<ImportJob>(entity =>
         {
             entity.Property(j => j.SourceRoot).IsRequired().HasMaxLength(1000);