feat(attachments): inject reference files into the run + clean up files on delete

TaskRunner appends attached files (absolute paths) to the run prompt as the
read-only Reference files section. Task and list deletes now remove the
on-disk attachment dir eagerly, and a startup AttachmentOrphanRecovery sweep
drops any attachments/<taskId>/ whose task no longer exists (covers list
cascade and planning-discard paths).

tests/ClaudeDo.Data.Tests/RepositoryAttachmentCleanupTests.cs

@@ -0,0 +1,85 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using Microsoft.EntityFrameworkCore;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Data.Tests;
+
+/// <summary>
+/// Verifies that TaskRepository.DeleteAsync and ListRepository.DeleteAsync
+/// delete the on-disk attachment directories for the affected tasks.
+/// </summary>
+public sealed class RepositoryAttachmentCleanupTests : IDisposable
+{
+    private readonly string _dbPath;
+    private readonly string _attachRoot;
+    private readonly ClaudeDoDbContext _ctx;
+    private readonly AttachmentStore _store;
+
+    public RepositoryAttachmentCleanupTests()
+    {
+        _dbPath = Path.Combine(Path.GetTempPath(), $"claudedo_repoclean_{Guid.NewGuid():N}.db");
+        _attachRoot = Path.Combine(Path.GetTempPath(), $"claudedo_repoclean_att_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_attachRoot);
+
+        var options = new DbContextOptionsBuilder<ClaudeDoDbContext>()
+            .UseSqlite($"Data Source={_dbPath}")
+            .Options;
+        _ctx = new ClaudeDoDbContext(options);
+        _ctx.Database.EnsureCreated();
+        _store = new AttachmentStore(_attachRoot);
+    }
+
+    public void Dispose()
+    {
+        _ctx.Dispose();
+        foreach (var suffix in new[] { "", "-wal", "-shm" })
+            try { File.Delete(_dbPath + suffix); } catch { }
+        try { Directory.Delete(_attachRoot, recursive: true); } catch { }
+    }
+
+    private async Task<(string listId, string taskId)> SeedAsync()
+    {
+        var listId = Guid.NewGuid().ToString();
+        var taskId = Guid.NewGuid().ToString();
+        _ctx.Lists.Add(new ListEntity { Id = listId, Name = "L", CreatedAt = DateTime.UtcNow });
+        _ctx.Tasks.Add(new TaskEntity
+        {
+            Id = taskId, ListId = listId, Title = "T",
+            Status = TaskStatus.Idle, CreatedAt = DateTime.UtcNow,
+        });
+        await _ctx.SaveChangesAsync();
+        return (listId, taskId);
+    }
+
+    [Fact]
+    public async Task TaskRepository_DeleteAsync_RemovesAttachmentDir()
+    {
+        var (_, taskId) = await SeedAsync();
+
+        var taskDir = _store.TaskDir(taskId);
+        Directory.CreateDirectory(taskDir);
+        Assert.True(Directory.Exists(taskDir));
+
+        var repo = new TaskRepository(_ctx, _store);
+        await repo.DeleteAsync(taskId);
+
+        Assert.False(Directory.Exists(taskDir));
+    }
+
+    [Fact]
+    public async Task ListRepository_DeleteAsync_RemovesAttachmentDirForEachTask()
+    {
+        var (listId, taskId) = await SeedAsync();
+
+        var taskDir = _store.TaskDir(taskId);
+        Directory.CreateDirectory(taskDir);
+        Assert.True(Directory.Exists(taskDir));
+
+        var repo = new ListRepository(_ctx, _store);
+        await repo.DeleteAsync(listId);
+
+        Assert.False(Directory.Exists(taskDir));
+    }
+}