feat(worker,ui): wire EF Core into DI and update all consumers to IDbContextFactory

Worker and App Program.cs: replace SqliteConnectionFactory+SchemaInitializer
with AddDbContextFactory<ClaudeDoDbContext> + Database.Migrate(). Repos
changed from AddSingleton to AddScoped.

All singleton services (QueueService, StaleTaskRecovery, WorktreeManager,
TaskRunner) and singleton ViewModels (MainWindowViewModel, TaskDetailViewModel,
TaskListViewModel, TaskEditorViewModel) now take IDbContextFactory<ClaudeDoDbContext>
and create short-lived contexts per operation.

Test infrastructure: DbFixture now uses EF migrations instead of SchemaInitializer;
all test classes create contexts via DbFixture.CreateContext().

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

tests/ClaudeDo.Worker.Tests/Infrastructure/DbFixture.cs

@@ -1,19 +1,30 @@
 using ClaudeDo.Data;
+using Microsoft.EntityFrameworkCore;
 
 namespace ClaudeDo.Worker.Tests.Infrastructure;
 
 public sealed class DbFixture : IDisposable
 {
     public string DbPath { get; }
-    public SqliteConnectionFactory Factory { get; }
 
     public DbFixture()
     {
         DbPath = Path.Combine(Path.GetTempPath(), $"claudedo_test_{Guid.NewGuid():N}.db");
-        Factory = new SqliteConnectionFactory(DbPath);
-        SchemaInitializer.Apply(Factory);
+        // Apply migrations so the schema is created.
+        using var ctx = CreateContext();
+        ctx.Database.Migrate();
     }
 
+    public ClaudeDoDbContext CreateContext()
+    {
+        var options = new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite($"Data Source={DbPath}")
+            .Options;
+        return new ClaudeDoDbContext(options);
+    }
+
+    public TestDbContextFactory CreateFactory() => new(this);
+
     public void Dispose()
     {
         try { File.Delete(DbPath); } catch { /* best effort */ }
@@ -21,3 +32,10 @@ public sealed class DbFixture : IDisposable
         try { File.Delete(DbPath + "-shm"); } catch { }
     }
 }
+
+public sealed class TestDbContextFactory : IDbContextFactory<ClaudeDoDbContext>
+{
+    private readonly DbFixture _fixture;
+    public TestDbContextFactory(DbFixture fixture) => _fixture = fixture;
+    public ClaudeDoDbContext CreateDbContext() => _fixture.CreateContext();
+}