docs(examples): show startup content capture with configure

[apucacao]

Adds a standalone example that turns conversation content on for the process with configure(options=SDKOptions(capture_content=True)) before init_client and the first AI call. The registered handlers are built with no capture_content argument.

It is not wired into main.py.

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Note

Overview
Adds a capture-content example that turns on process-wide conversation content capture with configure(options=SDKOptions(capture_content=True)) before the first config(...).invoke, using handlers from the global registry that do not set capture_content themselves (per-handler factory flags would override this default).

main.py registers the example under capture-content and documents the CLI usage alongside the other examples.

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[jeffdupont]

configure(options=SDKOptions(capture_content=...)) matches the lazy resolution in types.py (effective_capture_content), so calling it after handler registration is correct. Nit, non-blocking: this is the only example with its own __main__ instead of an entry in main.py.