Add offline-first task-master TUI with tickets, board lists, and undo.

Charm-based CLI with JSON persistence, status/list filters, external editor editing, command-history undo/redo, and glamour markdown without AutoStyle OSC hangs.

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

internal/command/command.go

@@ -0,0 +1,10 @@
+package command
+
+import "context"
+
+// Command is a reversible unit of work for future offline sync / undo trees.
+type Command interface {
+	Execute(ctx context.Context) error
+	Undo(ctx context.Context) error
+	Name() string
+}