feat(sounds): add brain-rot pack — 24 meme sounds across all 5 events

[adesai1000]

New pack: brain-rot 🧠

24 viral meme sounds ("brain rot" genre), mapped to event semantics:

Event	Sounds
session-start	Bing Chilling (good morning!), Among Us role reveal, Tung Tung Tung Sahur, Skibidi Toilet
task-acknowledge	"Let him cook!", Vine boom, "SHEEESH", "six seveeen!", "We do a little trolling"
task-complete	Anime wow, Taco Bell bong, MLG airhorn, Tralalero Tralala, "LET'S GOOO"
error	Metal pipe falling, bruh, "Emotional damage!", fart with reverb, AUGH, "erm, what the sigma?"
permission	"Chat, is this real?", "English or Spanish?", "Just put the fries in the bag", Among Us emergency meeting

Conventions followed

• Sourced from Myinstants, which the README already credits as a sound source.
• All clips trimmed to the repo's 8-second cap (longer clips get a 0.5s fade-out).
• Loudness-normalized to ~-35 LUFS integrated to match existing packs (measured warcraft/zelda/doom/mortal-kombat at -32 to -38 LUFS), so switching packs won't blast anyone's ears — ironic for brain rot, but kind.
• mp3 (libmp3lame VBR), kebab-case filenames, verified full-decode with ffmpeg.
• Tested end-to-end through scripts/play-sound.sh on macOS/afplay.

Docs updated

• README: pack table row + counts (63→64 packs, 552→576 sounds)
• package.json / .claude-plugin/plugin.json: description counts, brain-rot/memes keywords (version left untouched for the maintainer to bump)