🤖 fix: prevent model selection reset in creation mode

[ibetitsmike]

There were two issues causing the wrong model to be used when creating workspaces:

1. Stale React state: The handleSend callback in useCreationWorkspace captured sendMessageOptions from useSendMessageOptions, but that hook's state updates were delayed by requestAnimationFrame batching in usePersistedState. If the user selected a model and clicked send before the next animation frame, the old model value would be used.

2. Effect overwriting selection: The useEffect that initialized the model to the default when entering creation mode could re-run and overwrite the user's selection if defaultModel changed for any reason.

Fixes:

• Read send options fresh from localStorage at send time using getSendOptionsFromStorage instead of relying on potentially-stale React state
• Track initialization state with a ref so the model is only set once per entry into creation mode, not on every defaultModel change

Also added mode field to getSendOptionsFromStorage return value for parity with useSendMessageOptions.

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