fix/kim john ung prompt (#1446)

- **Update generated prompts**
- **Fix React error**
- **Don't show alpha apps during onboarding**
- **[Docs] First-class TanStack Start in AI setup prompts + clearer
env-var guidance (#1438)**
- **update docs**

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## Summary by CodeRabbit

* **Documentation**
* Simplified setup and environment-variable guidance across docs,
onboarding prompts, and setup snippets, replacing long explanatory
blocks with concise inline notes.
* Condensed frontend/backend examples into shorter combined examples and
streamlined cloud-project instructions.
* Shortened custom auth page prompts by removing verbose redirect/URL
override explanations and relying on shared reminder text.

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Author: mantrakp04