feat: right-click menus in Files/Users/Artifacts; several SSH keys and accounts per host

- Files: right-click a sidebar workspace (Open, Copy path) or home (Open,
  Open Trash), a path crumb (Open, Download as zip, Paste into, Copy path),
  a Trash row (Restore, Copy path, Delete forever), the Trash area (Refresh,
  Empty Trash) and an admin's per-user Trash folder (Open, Empty Trash).
- Users: row menu (Edit + Open home in Files for an admin, Copy username/email).
- Artifacts: card menu repeating its buttons, plus Copy link for a page.
- Git identity: named SSH keys beside the default ones (id_<type>_<name>,
  max 10, DELETE ?id=); SSH logins per alias (`ssh://<alias>/` →
  `ssh://<user>@<host>/`, so several AWS CodeCommit accounts share a host),
  each optionally tied to one key (`agenthub.<from>.sshKey`) — a clone of
  that URL offers only that key and persists it. Terminal sshCommand follows
  the keys. Settings → Git: "More SSH keys" + account name/key in the AWS and
  other-host forms. Docs/API.md, OpenAPI updated.

client/src/i18n/locales/en/artifacts.json

@@ -29,6 +29,7 @@
   "shareDone": "Shared to the Hub",
   "unshareDone": "Removed from the Hub",
   "open": "Open",
+  "copyLink": "Copy link",
   "preview": "Preview",
   "download": "Download",
   "install": "Install",