feat: copy task title to clipboard and add kanban lane view

[jwarykowski]

Summary

• y copies the selected item's title to the clipboard, wired up in the list, detail, and global views
• Promotes atotto/clipboard from an indirect to a direct dependency
• New lane view: one column per configured status, cycled to with v
• ←/→ switch the active column; tab moves the selected card into the next column and the cursor follows it
• Every existing field key (priority, category, tags, due, link, copy, edit, detail, toggle, delete) still acts on the lane-selected card
• All columns scroll together, centred on the active lane's cursor, via a scrollOffset helper extracted out of the existing list-view windowing
• Not available in the global view, since different boards can configure different statuses
• Fixes a latent bug in the footer's help-grid column padding (byte length instead of display width), surfaced by the new arrow-glyph key hint

Test plan

• gofmt -l . / go vet ./... / go build / go test ./... / golangci-lint run all clean
• New tests: copy-title from list/detail/global, cycling into lane view, left/right column switching with clamping, cursor confined to the active column, tab moving a card with the cursor following, a mutation key acting on the lane-selected card, and scroll behaviour with more cards than fit
• Manually driven in a live TUI session against a scratch board