ui: read persisted settings before the API key probe (#27365)
The route loads run ahead of the root layout script, so validateApiKey
read the settings store while it still held factory defaults and probed
/props without the stored key. initStores() now hands the same startup
promise to every caller and the chat loads await it before probing.
The one-time admin baseline no longer overwrites a key the user has
already set: on a first visit the config carries factory values only, so
a diverging key comes from the user and wins.
