Honor explicit AUTO_INDENT false in prompt modes

[OskarEichler]

Summary

Read the prompt mode's AUTO_INDENT value after checking key presence, so an explicit false disables indentation instead of becoming true.

Reproduction

A prompt configuration containing AUTO_INDENT: false currently stores the result of Hash#include?, which is true. The candidate stores the configured value.

Verification

• current and cumulative candidate suites: 402 tests / 2,488 assertions, zero failures/errors and three omissions
• all 111 Ruby files pass syntax
• RuboCop checks 113 files with no offenses
• RDoc and Rails 8.1.3.1 loading pass

Compatibility

Only explicit false prompt configuration changes, to match its documented intent. Prepared with AI-assisted source review; no repository tests were changed.

[tompng]

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