Complete the read and update faces of the signed-in user's attachment
management over the existing attachments table:
- GET /uploads: paginated list of the user's own attachments, newest
first, with an optional linked/orphaned filter
- GET /uploads/{uid}: fetch one attachment (owner or admin)
- PATCH /uploads/{uid}: rename the display filename, always preserving
the original extension (owner or admin, audited as attachment.rename)
Adds get_user_attachments/get_user_attachment data helpers, the
rename_attachment operation, AttachmentRenameForm, the UploadItemOut and
UploadsListOut schemas, the Devii tools list_attachments/get_attachment/
rename_attachment, expanded API reference documentation for the full
lifecycle including delete, and api-tier tests.
