Re-source the Prickly Pear sticker pack

Background

The chat emoji picker used to ship a 46-sticker pack called Prickly Pear (a Facebook Messenger sticker set, names like `cactus_bird`, `cactus_happy`, `cactus_kiss`, etc.). Every entry pointed at `https://downforacross.s3-us-west-1.amazonaws.com/stickers/`, which is the legacy downforacross's S3 bucket — gone / inaccessible. Every emoji in the pack rendered as a broken-image placeholder.

The pack file (`src/lib/emojiPacks/pricklyPear.json`) and its wiring in `src/lib/emoji.js` were dropped to stop surfacing the broken references. See PR with the removal.

What this issue is for

Re-source the 46 stickers so we can ship the pack again, this time self-hosted.

Recovery path

1. Find the source. The original pack is a Facebook Messenger sticker pack ("Prickly Pear", cactus character). The legacy app scraped it via yolandaz/stickers — that tool's repo is also 404 now.
   • If the pack still exists on Messenger, manually saving each sticker is the simplest path (~30 min).
   • The full list of 46 names is in the git history of `pricklyPear.json`.
2. Host them locally, following the `partyParrot` pack's pattern:
   • Drop the PNGs in `public/emojis/pricklyPear/.png`
   • Add `src/lib/emojiPacks/pricklyPear.js` using `parseRawUrls` (see `src/lib/emojiPacks/partyParrot.js`)
   • Re-add the import + spread in `src/lib/emoji.js`
3. Verify: pack shows up in the chat emoji picker, all 46 render, no 404s in the network tab.

Why this is good-first-issue

• Isolated to one feature
• No backend or schema changes
• Mostly a "find the assets" + small JS wiring task
• Easy to test locally (`pnpm start`, open chat, type `:cactus`)

Acceptance

• All 46 emoji from the pack render correctly in the chat picker
• Assets are checked into the repo (no external CDN dependency)
• No 404s in browser network tab for any pricklyPear emoji