docs: simplify the Anthropic quickstart (#5979)

Make the Anthropic quickstart short and noninteractive: use one-sentence
task and system prompts, `claude-opus-5-5` directly, and a commented
`use_cloud=True` option. Keep all 31 browser actions plus Bash enabled;
the quickstart deliberately uses a one-line automatic-approval callback
instead of terminal prompts. Local upload policy still applies.

Move the interactive confirmation example and diagram to the final
Approvals section. Keep earlier remote-upload examples independent of
that later function, and distinguish page JavaScript from raw CDP
programming.

Validation: pre-commit passed; integration tests 11 passed / 1 skipped;
five SDK callback/policy checks passed, including automatic approval,
denied outside-root uploads, and the later allow/decline/error examples.
All Python snippets compile and the three quickstart copies match. Model
ID verified against Anthropic's browser-toolset documentation:
https://platform.claude.com/docs/en/agents-and-tools/tool-use/browser-use-tool
. No live model or benchmark run.


<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Makes the Anthropic quickstart runnable non-interactively so users get a
working example without prompts or extra configuration.

- Shortens the task and system prompts to single sentences, pins
`claude-opus-5-5`, and drops the `ANTHROPIC_MODEL` env var requirement.
- Replaces the interactive approval callback with `confirm=lambda _:
True`; the interactive example, diagram, and policy details moved to a
new Approvals section.
- Adds a commented `use_cloud=True` option and updates the integration
test to expect the auto-approval lambda.

<sup>Written for commit d018a0e2ba58a347f7e74bbb0a8566b6377ada77.
Summary will update on new commits.</sup>

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