Guard Assets Manager option saves

[mehul0810]

Summary

• Guards Assets Manager save payloads and stored option reads before nested access.
• Preserves the existing perform_assets_manager_options storage shape and option names.
• Fixes archive exception persistence to store the selected archive value instead of reading an unrelated variable.

Validation

• php -l src/Modules/Assets/AssetsManager.php
• composer check-cs -- src/Modules/Assets/AssetsManager.php
• git diff --check
• Local Studio save-flow smoke on ?perform=1 persisted {"disabled":{"js":{"hoverintent-js":{"current":[0]}}}}, then test options were removed.

Closes #26.

[github-actions]

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