Keyboard-operable modal dialog with focus trap and return

Build a single self-contained page as one HTML file (`index.html`) that renders with no build step and no network calls (inline all CSS and JS, no external fonts or scripts). The page has a trigger button with id="open-dialog" and the visible text "Subscribe". Activating that button (by mouse OR by keyboard) opens a modal dialog. Requirements: - The dialog container has role="dialog" and aria-modal="true". The trigger carries aria-expanded, "false" while the dialog is closed and "true" while it is open. - When the dialog opens, keyboard focus moves into the dialog (to the first focusable control inside it). The dialog must contain an email input with id="email", a Cancel button with id="cancel", and a confirm button with id="confirm". - While the dialog is open, Tab and Shift+Tab are TRAPPED inside the dialog: tabbing past the last control wraps to the first, and shift-tabbing past the first wraps to the last. Focus never lands on the page behind the dialog. - Pressing Escape (or activating Cancel) closes the dialog AND returns keyboard focus to the trigger button (id="open-dialog"). The dialog must be fully operable with the keyboard alone. Use plain, readable, accessible markup. Seed real-looking copy.