WWT is not quite ready when promise resolves

[Carifio24]

The WWT Pinia store offers the (extremely useful) waitForReady method that can be awaited to make sure that code only runs when WWT is ready. However, there are a few methods that will cause errors if invoked immediately after the store is ready. As a simple example of this, modify the research app mounted hook to be the following:

this.waitForReady().then(() => {
  console.log(this.findScreenPointForRADec({ ra: 10, dec: 20 }));
  // ...
});

then load up the app and you'll get a fun error like

Cannot read properties of undefined (reading 'get__isDistinguishedIdentity')
TypeError: Cannot read properties of undefined (reading 'get__isDistinguishedIdentity')
    at __webpack_modules__../esm/double3d.js.Matrix3d.multiplyMatrix (webpack-internal:///../engine/src/index.js:11645:17)
    at WWTControl.transformWorldPointToPickSpace (webpack-internal:///../engine/src/index.js:61047:68)
    at WWTControl.getScreenPointForCoordinates (webpack-internal:///../engine/src/index.js:61060:27)
    at Proxy.eval (webpack-internal:///../engine-pinia/dist/index.umd.js:6601:44)
    at eval (webpack-internal:///../node_modules/ts-loader/index.js??clonedRuleSet-40.use[0]!../node_modules/vue-loader/dist/index.js??ruleSet[0].use[0]!./src/App.vue?vue&type=script&lang=ts:2055:31)

which we get because the render context matrices haven't been set up yet.

The obvious solution to this is to force-render a frame before we report from the store that WWT is ready, but maybe there's a better approach? Pinging @pkgw in case he has any thoughts.