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).
TaskAttachmentEntity (+config, cascade FK), TaskAttachmentRepository, and an
AttachmentStore that writes files under ~/.todo-app/attachments/<taskId>/ with
a path-traversal guard and a 5 MB cap. TaskPromptComposer gains an optional
read-only 'Reference files' section. Migration AddTaskAttachments.
Mika Kuns