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).

src/ClaudeDo.Data/AttachmentStore.cs

@@ -9,6 +9,18 @@ public sealed class AttachmentStore
     public AttachmentStore(string? root = null)
         => _root = root ?? Paths.Expand("~/.todo-app/attachments");
 
+    public string Root => _root;
+
+    public IReadOnlyList<string> EnumerateTaskIds()
+    {
+        if (!Directory.Exists(_root)) return Array.Empty<string>();
+        return Directory.GetDirectories(_root)
+            .Select(Path.GetFileName)
+            .Where(n => n is not null)
+            .Select(n => n!)
+            .ToList();
+    }
+
     public string TaskDir(string taskId)
         => Path.Combine(_root, taskId);
 

src/ClaudeDo.Data/Repositories/ListRepository.cs

@@ -6,8 +6,13 @@ namespace ClaudeDo.Data.Repositories;
 public sealed class ListRepository
 {
     private readonly ClaudeDoDbContext _context;
+    private readonly AttachmentStore _attachments;
 
-    public ListRepository(ClaudeDoDbContext context) => _context = context;
+    public ListRepository(ClaudeDoDbContext context, AttachmentStore? attachments = null)
+    {
+        _context = context;
+        _attachments = attachments ?? new AttachmentStore();
+    }
 
     public async Task AddAsync(ListEntity entity, CancellationToken ct = default)
     {
@@ -23,7 +28,13 @@ public sealed class ListRepository
 
     public async Task DeleteAsync(string listId, CancellationToken ct = default)
     {
+        var taskIds = await _context.Tasks
+            .Where(t => t.ListId == listId)
+            .Select(t => t.Id)
+            .ToListAsync(ct);
         await _context.Lists.Where(l => l.Id == listId).ExecuteDeleteAsync(ct);
+        foreach (var id in taskIds)
+            _attachments.DeleteTaskDir(id);
     }
 
     public async Task<ListEntity?> GetByIdAsync(string listId, CancellationToken ct = default)

src/ClaudeDo.Data/Repositories/TaskRepository.cs

@@ -7,8 +7,13 @@ namespace ClaudeDo.Data.Repositories;
 public sealed class TaskRepository
 {
     private readonly ClaudeDoDbContext _context;
+    private readonly AttachmentStore _attachments;
 
-    public TaskRepository(ClaudeDoDbContext context) => _context = context;
+    public TaskRepository(ClaudeDoDbContext context, AttachmentStore? attachments = null)
+    {
+        _context = context;
+        _attachments = attachments ?? new AttachmentStore();
+    }
 
     #region CRUD
 
@@ -37,6 +42,7 @@ public sealed class TaskRepository
     public async Task DeleteAsync(string taskId, CancellationToken ct = default)
     {
         await _context.Tasks.Where(t => t.Id == taskId).ExecuteDeleteAsync(ct);
+        _attachments.DeleteTaskDir(taskId);
     }
 
     public async Task<TaskEntity?> GetByIdAsync(string taskId, CancellationToken ct = default)