Open and render a Mini App in the workspace panel #256

Parent

#251

What to build

A person can see the Mini Apps they have installed and open one into the workspace panel, where its page
renders and its bridge reaches the host. The runtime service is enabled for this client in this change.

Acceptance criteria

• The plugin catalogue's apps area lists installed Mini Apps with their runtime state and offers
  install, uninstall, enable, disable, stop and open.
• A launcher tile in the workspace panel opens a picker fed by the same listing.
• Choosing one opens a workspace panel tab for the current session and renders that Mini App's page.
• The page can append a draft to the composer after a confirmation, and declining leaves the
  existing draft untouched.
• Opening a fourth Mini App while three run names the running ones and lets the person stop one.
• A Mini App another client owns is reported in the apps area and in the picker, naming that client,
  instead of failing silently (moved here from One client owns a Mini App at a time #254).
• With explicit Mini App options and no declared owner kind, the service starts a Mini App through the
  open operation and produces its view URL, which the panel frames (moved here from Serve a Mini App page through its own proxy #255).
• The service is enabled for this client's runtime owner through the policy cell, the capability
  flag agrees with the service, and the explicit-options override still works.
• A Mini App that the agent starts is displayable, so no state exists in which the capability is on
  and nothing can show a Mini App.
• A stopped runtime clears the view and reports why, and nothing reconnects without a user action.
• Mini App client state lives in one business; the plugin catalogue and the workspace panel hold
  none of it.