fix: small audit follow-ups across 7tv, youtube autocomplete, emote modal and hover effects

[dclstn]

Four small fixes from an audit of 7.7.25 to master, none of them worth a PR each:

• 7TV update events: the updated and pulled loops in channel-emotes.js used return where their sibling uses continue, so one emote BetterTTV didn't know about aborted the rest of that event, including every pull after it.
• YouTube command autocomplete: updateFocusListener added a new bound focus listener without removing the previous one, so each reload while dirty stacked another. Now mirrors the Twitch version: remove first, then add if still needed.
• Emote modal availability: a second failed lookup merged the unknown sentinel into a plain {}, which fetchAvailability then treated as a cache hit for the rest of the session. The merge now treats a sentinel in the cache as empty, so repeated failures stay retryable.
• Hover effects under Reduce Motion: the JS check only ran when the class was applied, so turning Reduce Motion on mid-session left already-rendered names hopping, scaling and flipping. .reducedMotion rules now cover .wave, .bounce and .flip too.

Verification: reasoned from the code, lint and build pass. The CSS is specificity-checked against the hover rules it overrides but not exercised live.

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