Add per-workspace auto-incrementing issue numbers with a configurable
prefix, producing identifiers like "JIA-1" instead of truncated UUIDs.
Database:
- Add issue_prefix and issue_counter to workspace table
- Add number column to issue table with UNIQUE(workspace_id, number)
- Backfill existing issues with sequential numbers
Backend:
- Issue creation atomically increments counter in a transaction
- API responses include number and identifier fields
- Support issue lookup by identifier format (KEY-N)
- Workspace prefix auto-generated from name, customizable via API
Frontend:
- Display identifier in list rows and issue detail breadcrumb
- Add issue_prefix to Workspace type, number/identifier to Issue type
