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/ticket/editfile_editor_test.go

@@ -0,0 +1,34 @@
+package ticket_test
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+
+	"task/internal/ticket"
+)
+
+func TestResolveEditorPrefersEnv(t *testing.T) {
+	t.Setenv("EDITOR", "custom-ed")
+	t.Setenv("VISUAL", "visual-ed")
+	if got := ticket.ResolveEditor(); got != "custom-ed" {
+		t.Fatalf("got %q, want custom-ed", got)
+	}
+}
+
+func TestResolveEditorFallsBackToNvim(t *testing.T) {
+	t.Setenv("EDITOR", "")
+	t.Setenv("VISUAL", "")
+	got := ticket.ResolveEditor()
+	if _, err := exec.LookPath("nvim"); err == nil {
+		if got != "nvim" {
+			t.Fatalf("got %q, want nvim when available", got)
+		}
+		return
+	}
+	// Without nvim, accept vim/vi.
+	if got != "vim" && got != "vi" {
+		t.Fatalf("got unexpected fallback %q", got)
+	}
+	_ = os.Environ()
+}