docs: refresh docs and examples to gpt-5.4

[seratch]

This pull request updates English docs and user-facing examples to prefer gpt-5.4 over older gpt-5.2 references across guides, AI SDK samples, basic examples, memory samples, and tool examples.

It keeps stable example filenames such as gpt-5.ts while refreshing the underlying model names and accompanying prose in the models and voice-agents guides. It also tightens the apply-patch example for gpt-5.4 by adding low reasoning effort and a more explicit in-place edit prompt after live validation showed malformed patch context without that extra guidance.

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