fix: resolve verifiable bugs in other-amount.ts and src-defer.ts

[bryancasler]

This PR resolves the following verifiable bugs identified during code audit by MinMax M2.5:

Bugs Fixed

1. other-amount.ts - Invalid event type in addEventListener (HIGH)

   • Issue: String event names ('focusin', 'input') were passed directly to addEventListener() without type assertion
   • Fix: Added proper type assertion for the event parameter

2. other-amount.ts - Potential null reference (MEDIUM)

   • Issue: lastRadioInput could be null if the selector didn't match, causing runtime error when setting .checked
   • Fix: Added null check before accessing .checked property

3. src-defer.ts - Incorrect replaceChild arguments (CRITICAL)

   • Issue: replaceChild was passing the same element twice (copy = original), and subsequent video property modifications were applied to the removed element
   • Fix: Properly clone the video element using cloneNode(true), replace the original with the clone, and apply modifications to the cloned element

Testing

All changes compile successfully with TypeScript." 2>&1

[fernanDOTdo]

@bryancasler Please, create a test page where we can see and understand each one of the issues and validate the solutions.
Thank you!