feat(admin): copy buttons and shared clipboard helper

- Add magesail-clipboard.js (clipboard API + execCommand fallback)
- Tunnel: copy store code, key, Holesail command, log tail; wire polling UI
- How-To: copy per code block; Howto block + magesail-howto-copy.js
- NGINX map: copy raw map from textarea; translations in Map block
- Document copy UX in docs/admin-ui.md

Magesail/Block/Adminhtml/Nginx/Map.php

@@ -87,6 +87,9 @@ class Map extends Template
                 'yes' => (string) __('Yes'),
                 'no' => (string) __('No'),
                 'diagIssue' => (string) __('Issue:'),
+                'copyRawMap' => (string) __('Copy raw map'),
+                'copied' => (string) __('Copied!'),
+                'copyFailed' => (string) __('Copy failed'),
             ],
         ];
     }