Add multiselect board filters and letter-jump on picker menus.

Persist comma-separated list filters per project, toggle with space, and jump by first letter in board and project pickers.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/ui/helpbar.go

@@ -30,6 +30,7 @@ func (m Model) helpEntries() []helpEntry {
 	case ModeProjects:
 		return []helpEntry{
 			{"j/k", "navigate"},
+			{"a-z", "jump"},
 			{"enter", "select"},
 			{"n", "new project"},
 			{"esc", "cancel"},
@@ -43,7 +44,9 @@ func (m Model) helpEntries() []helpEntry {
 		}
 	case ModeBoard:
 		return []helpEntry{
-			{"j/k", "select"},
+			{"j/k", "navigate"},
+			{"a/b/i/d", "jump"},
+			{"space", "toggle"},
 			{"enter", "apply"},
 			{"esc", "cancel"},
 		}