Fix: expand HTML attachment iframe height (#706)

[SilviuM88]

Summary

Adjusts iframe resizing logic and CSS to ensure HTML attachments expand to their content height.

Changes

• allure-commandline/custom-iframe-resize.js: measure/resize to content height
• allure-commandline/custom-styles.css: complementary styling fixes

Issue

Fixes #706

Notes

• Only two files touched. No build artifacts included.
• If this contribution aligns with the project’s goals, I’d kindly appreciate if you could tag it as hacktoberfest-accepted. Thank you!

[CLAassistant]

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