Add claude cache control docs

[reynaldichernando]

• add prompt caching section in ai chat docs (only anthropic for now)
• add example
• add playground example

[Copilot]

Pull request overview

Adds documentation and a runnable playground example demonstrating Anthropic/Claude prompt caching via cache_control, so readers can understand and try cost/latency optimization for repeated long prompts within the Puter.js AI chat API docs.

Changes:

• Added a new playground HTML example showing cache_control: { type: "ephemeral" } on a long system prompt.
• Registered the new example in the docs examples index for discoverability in the playground.
• Expanded AI/chat.md with a “Prompt Caching” section and an accompanying example snippet + links.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
src/docs/src/playground/examples/ai-claude-cache-control.html	New runnable playground example demonstrating Claude prompt caching.
src/docs/src/examples.js	Adds the new example to the AI examples list.
src/docs/src/AI/chat.md	Adds prompt caching documentation and includes the new example + references.

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