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>

store.go

@@ -120,6 +120,8 @@ type Settings struct {
 	Sandbar      SandbarSync `json:"sandbar"`
 	// SelfEdgeID is this server's own edge (see HAMMERHEAD_SELF_DOMAIN).
 	SelfEdgeID string `json:"selfEdgeId,omitempty"`
+	// Terminal holds the web terminal's SSH key and the host keys it has seen (see terminal.go).
+	Terminal TerminalSettings `json:"terminal"`
 }
 
 type Secret struct {