Tasks can now carry file attachments (PDFs, images, source docs) that
workers read directly — closes the gap where source material had to be
pasted as a path into the task body.
- kanban_db: task_attachments table (additive), Attachment dataclass,
add/list/get/delete accessors, attachments_root/task_attachments_dir
path helpers (per-board, HERMES_KANBAN_ATTACHMENTS_ROOT override)
- build_worker_context: surfaces each attachment's absolute path so the
worker (full file/terminal tool access) reads it via read_file/pdftotext
- dashboard API: POST/GET/DELETE attachment routes (multipart upload,
25MB cap, traversal-safe filenames, root-containment check on download)
- dashboard UI: Attachments section in the task drawer — upload button,
list with download, per-row remove
- docs + tests (13 cases: DB accessors, REST round-trip, traversal
rejection, collision suffixing, worker-context surfacing)
Closes#35338
b47cb1bbf2