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/layout.go

@@ -12,7 +12,7 @@ import (
 func (m Model) renderHeader() string {
 	brand := m.styles.HeaderBrand.Render(config.AppName)
 	project := m.styles.HeaderMeta.Render(fmt.Sprintf("project: %s", m.cfg.ActiveProject))
-	board := m.styles.FilterHint.Render(fmt.Sprintf("list: %s", m.boardList.Label()))
+	board := m.styles.FilterHint.Render(fmt.Sprintf("list: %s", m.boardFilter.Label()))
 	count := m.styles.HeaderMeta.Render(fmt.Sprintf("%d tickets", m.ticketCount()))
 
 	parts := []string{brand, project, board, count}