vscode: Cloud account + tower registration UI in the Codev sidebar

[amrmelsayed]

Depends on the Codev AuthenticationProvider issue. Surfaces the existing Tower⇄Cloud registration (today CLI-only: `afx tower connect`, which writes `~/.agent-farm/cloud-config.json`) as first-class UI.

Scope

1. Signed-out: unobtrusive sign-in affordance in the Codev container (gate placement via the existing context-key matrix; never a startup prompt).
2. Signed-in: account row (email/plan), this Tower's cloud status (registered? tunnel up?), and a Connect Tower to Cloud command.
3. The connect command must DRIVE the existing CLI/Tower registration path rather than reimplement it — `cloud-config.json` stays the single source of truth for tower credentials (`ctk_` keys never duplicated into extension storage).
4. Disconnect/re-register flows with confirmation.

Acceptance

• Fresh account → connect Tower → cloud dashboard shows the tower; all without a terminal.
• Guest-mode marketplace users see identical capability (this is not IDE-gated); signed-out UX unchanged from today except the affordance.