Consistent menu on gardens#show

[Br3nda]

Part of the "Consistent menus across the site" epic (#4839).

Bring gardens#show into line with the site-wide actions-menu convention:

• One actions menu on the page, and only one
• It is an icon-only three-dot (kebab) button, fas fa-ellipsis-vertical, with aria-label="Actions" and a tooltip
• Pinned to the top right of the page hero, on the same line as the title
• .dropdown-menu.dropdown-menu-end so it opens leftward and does not overflow on narrow screens
• Items in the standard order: edit, add photo, state changes, divider, delete last and text-danger
• Rendered only when can?(:edit, record) — never disabled-but-visible
• No nested dropdowns and no forms inside the menu; anything needing a form opens a dialog (see Use modal overlay forms across the site, updating in place #4838)
• Button variants audited: no btn-info for actions, no bare btn with no variant

Check how this interacts with the garden card menus on gardens#index, which already use ActionsMenu.jsx.