With .ykanban present but ykanban.db gone, opening used to create an empty
database and show an empty board without any hint. It now throws
WorkspaceDatabaseMissingException and shows the open-failed page, telling the
user to restore a backup or delete .ykanban and initialize again.
- board: columns in id order, per-column sort via config, column width presets (240/320/480) and custom 160-720
- column header new-card and edit/delete menu; card menu delete and move-to-column
- card editor as one unit of work with dirty check and discard confirmation; nested tag picker writes new tags immediately
- schema constraint violations mapped to typed exceptions and shown inside the modal
- dialog service with owner stack so nested modals center on their parent and get FlowDirection
- repository: filtered GetCards, CountCards; view-model tests
doyaGu