Summary

Kanban dashboard currently lacks batch selection and multi-card operations. Users must move or update cards one at a time, and the search bar only matches title/assignee rather than full card contents.

Repro / Why this matters

• Moving 10+ "ready" tasks to "running" requires 10+ individual drag operations
• Reassigning multiple tasks at once is impossible — the bulk endpoint exists but the UI does not expose it
• Searching for a task by its body text or run summary does not work, forcing users to open cards individually

Proposed fix

1. Batch card selection: shift-click range selection, column select-all toggle, select-all-visible
2. Multi-card drag & drop: drag any selected card to move the entire selection via the existing /tasks/bulk endpoint
3. Expanded bulk actions bar: todo / ready / blocked / unblock / complete / archive, priority setter, reassign with optional reclaim_first checkbox
4. Partial-failure highlighting: cards that fail during bulk operations are marked with CSS class hermes-kanban-card--failed
5. Search expansion: include body, result, and latest_summary in the client-side search haystack
6. Clear filters button + auto-reset on board switch
7. Accessibility: larger checkbox hit targets, tabIndex / role / aria-label, Enter/Space/Esc keyboard handlers

Scope

• Only plugins/kanban/dashboard/ frontend changes
• Backend change: extend BulkTaskBody with reclaim_first: bool = False to match the single-task /tasks/{id}/reassign reclaim behavior
• No changes to kanban DB schema, dispatch daemon, or worker lifecycle
• No unrelated features bundled

Validation

• scripts/run_tests.sh tests/plugins/test_kanban_dashboard_plugin.py
• Manual: open dashboard, shift-select 3 cards, drag to another column, verify N-card ghost badge and dimming
• Manual: use bulk action bar to reassign with reclaim_first checked, verify running tasks are reclaimed before reassignment