Fix: Correct backup codes usage statement for all affected versions (Product IS issue #25714)

[wso2-engineering-bot]

This PR was automatically generated by Claude AI.

• Issue: Incorrect statement regarding usage of backup codes in SMS OTP documentation product-is#25714
• Type: Documentation (Bug fix)
• Summary: Corrected misleading statement about backup codes usage in SMS OTP documentation. Backup codes are intended as a fallback when SMS OTP is enabled but temporarily inaccessible, not when SMS OTP is disabled.
• Affected Versions: 6.0.0, 6.1.0
• Style Scope Verification: Microsoft Style Guidelines have been applied only to newly added content without modifying existing content style.
• Verification: mkdocs build --strict completed without introducing new errors. Pre-existing warnings unrelated to this fix remain.

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