update README action caching

[Dingway98]

Note

Adds comprehensive Action Caching documentation and examples, updates Anthropic/Gemini model configs, fixes the custom actions example, and refreshes documentation links.

• Docs (README):
  • Action Caching: New section detailing recording during page.ai(), deterministic replay via runFromActionCache(), script generation with createScriptFromActionCache(), and key use cases.
  • LLM Config Updates:
    • Anthropic model updated to claude-sonnet-4-0.
    • Gemini model updated to gemini-2.5-flash.
  • Custom Actions Example:
    • Fix action schema description/comma error and parameter typing ({ search: string }).
    • Correct success message typo and add executeTask usage example.
  • Links:
    • Add top-level docs link to https://www.hyperbrowser.ai/docs/hyperagent/introduction.
    • Update Support docs link to .../hyperagent/introduction.
  • Minor text polish (e.g., apostrophes) and formatting adjustments.

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