fix(content): only remove .fbc-wrapper when one already existed

[SAY-5]

Summary

Closes #1008.

openInputPrompt queries for an existing .fbc-wrapper and, when one is missing, injects a fresh wrapper into the page. The trailing call

hasFbcWrapper.remove();

was placed outside the if/else block, so it ran unconditionally, including on the first badge click of a page when no wrapper existed and one was just created. The result was

TypeError: hasFbcWrapper is null
    at openInputPrompt (src/content_script.js:331)

and the prompt failed to open until a second click rebuilt the missing branch.

Fix

Move hasFbcWrapper.remove() into an else branch so it only runs when an existing wrapper is being torn down to make room for the new injection.

if (!hasFbcWrapper) {
    document.body.appendChild(injectIframeOntoPage(...));
    ...
} else {
    hasFbcWrapper.remove();
}

Test plan

• node -c src/content_script.js, passes
• Manual: load the extension, click any Facebook login badge as the very first interaction on a fresh page, confirm the in-page prompt opens without a console TypeError