fix: resolve 4 bugs in TourEase

[saurabhhhcodes]

Description

This PR fixes real bugs found in the codebase:

• Replaced innerHTML assignment with textContent: prevents HTML injection / XSS and is faster since it does not parse markup.
• Replaced global isNaN with Number.isNaN: the global version coerces its argument, so isNaN('1') returns false while Number.isNaN is strict.
• Added explicit radix to parseInt: without 10, strings like '0x1F' or '08' parse in unintended bases.
• Removed return undefined: bare return conveys the same intent without the redundant literal.

Type of Change

• Bug fix (non-breaking change fixing an issue)

How Has This Been Tested?

• Local manual testing

Checklist

• My code follows the style guidelines
• I have performed a self-review

Related Issue

Ref: #862

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