chore(data): remove raw ADO.NET infrastructure, add EF migration and design-time factory

Delete SqliteConnectionFactory, SchemaInitializer, and schema.sql.
Fix ValueConverter lambdas in entity configurations (no throw-expressions
in expression trees). Add IDesignTimeDbContextFactory for dotnet-ef tooling.
Generate InitialCreate migration with seed data for agent/manual tags.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ClaudeDo.Data/Configuration/WorktreeEntityConfiguration.cs

@@ -1,11 +1,29 @@
 using ClaudeDo.Data.Models;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
 
 namespace ClaudeDo.Data.Configuration;
 
 public class WorktreeEntityConfiguration : IEntityTypeConfiguration<WorktreeEntity>
 {
+    private static string StateToString(WorktreeState v)
+        => v == WorktreeState.Active ? "active"
+         : v == WorktreeState.Merged ? "merged"
+         : v == WorktreeState.Discarded ? "discarded"
+         : v == WorktreeState.Kept ? "kept"
+         : throw new ArgumentOutOfRangeException(nameof(v));
+
+    private static WorktreeState StateFromString(string v)
+        => v == "active" ? WorktreeState.Active
+         : v == "merged" ? WorktreeState.Merged
+         : v == "discarded" ? WorktreeState.Discarded
+         : v == "kept" ? WorktreeState.Kept
+         : throw new ArgumentOutOfRangeException(nameof(v));
+
+    private static readonly ValueConverter<WorktreeState, string> StateConverter =
+        new(v => StateToString(v), v => StateFromString(v));
+
     public void Configure(EntityTypeBuilder<WorktreeEntity> builder)
     {
         builder.ToTable("worktrees");
@@ -19,23 +37,7 @@ public class WorktreeEntityConfiguration : IEntityTypeConfiguration<WorktreeEnti
         builder.Property(w => w.DiffStat).HasColumnName("diff_stat");
         builder.Property(w => w.State).HasColumnName("state").IsRequired()
             .HasDefaultValue(WorktreeState.Active)
-            .HasConversion(
-                v => v switch
-                {
-                    WorktreeState.Active => "active",
-                    WorktreeState.Merged => "merged",
-                    WorktreeState.Discarded => "discarded",
-                    WorktreeState.Kept => "kept",
-                    _ => throw new ArgumentOutOfRangeException()
-                },
-                v => v switch
-                {
-                    "active" => WorktreeState.Active,
-                    "merged" => WorktreeState.Merged,
-                    "discarded" => WorktreeState.Discarded,
-                    "kept" => WorktreeState.Kept,
-                    _ => throw new ArgumentOutOfRangeException()
-                });
+            .HasConversion(StateConverter);
         builder.Property(w => w.CreatedAt).HasColumnName("created_at").IsRequired();
     }
 }