Web terminal: open a shell on a site from the dashboard

Hammerhead signs in to the site's Bamboo SSH server through the SSH port an edge
exposes, with a key of its own, and relays the shell to the browser over a
WebSocket (xterm.js, served by Hammerhead). The SSH dialog shows Hammerhead's
public key to add to authorized_keys. Host keys are saved on first use and a
changed one is refused; the terminal opens only from the dashboard's own
origin, is audited, and closes after 30 minutes idle. Errors reach the page as
messages over the socket. An end-to-end test runs a real shell through the
edge, tunnel and Bamboo.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server.go

@@ -45,6 +45,10 @@ func (s *Server) Handler() http.Handler {
 
 	s.registerAlertRoutes(mux)
 	mux.HandleFunc("GET /metrics", s.metrics)
+	mux.Handle("GET /static/term/", terminalStatic())
+	mux.HandleFunc("GET /api/orgs/{org}/terminal", s.withOrg(true, s.terminalKey))
+	mux.HandleFunc("GET /api/orgs/{org}/sites/{id}/terminal", s.withOrg(true, s.siteTerminal))
+	mux.HandleFunc("DELETE /api/orgs/{org}/sites/{id}/terminal/hostkey", s.withOrg(true, s.forgetHostKey))
 
 	// public
 	mux.HandleFunc("GET /api/public", s.publicInfo)