ref: unify endpoints handling in the client

[krystofwoldrich]

• Based on fix: route sim client requests via base path #18

This refactors the preview config from a flat object into a small route manifest. The important change is that middleware routes and helper routes are now separate.

/api, /exec, /logs, and /appstate come from the host middleware under the configured preview base path.

/stream.mjpeg, /ws, and /config come from the per-device Swift helper on its own localhost port.

The new config shape is roughly:

{
  basePath: "/.sim",
  endpoints: {
    api: "/.sim/api",
    exec: "/.sim/exec",
    logs: "/.sim/logs?device=...",
    appState: "/.sim/appstate?device=..."
  },
  helper: {
    url: "http://127.0.0.1:3100",
    stream: "http://127.0.0.1:3100/stream.mjpeg",
    ws: "ws://127.0.0.1:3100/ws",
    config: "http://127.0.0.1:3100/config"
  }
}

This also injects the preview config even when no helper is running, so the empty state can still call middleware endpoints
like /exec.