feat(BetterGifs): add KLIPY as a provider

[IzieStratt]

Adds KLIPY next to Tenor and Giphy in the Better GIFs provider switch (settings and the picker dropdown). Tenor stays the default.

• New "KLIPY API key" text setting. KLIPY needs a per-app key and there's no keyless proxy like tenor-proxy, so users bring their own free key from partner.klipy.com. With no key set, the picker says so instead of failing silently.
• Search and trending use KLIPY's /gifs/search and /gifs/trending endpoints. Results are mapped into the existing Gif type (md gif for the message, sm gif for the preview), ads are skipped, and favorites work the same as for Tenor.
• Search cache is per provider and cleared when settings change.
• Tests added for response mapping, favorites validation and request building. oxlint, oxfmt, typecheck and the BetterGifs tests pass.

How to get a KLIPY key (about a minute, free)

1. Go to https://partner.klipy.com and sign in or sign up.
2. Click "Add Platform", fill in a name, your email, a website and a one-line description, then accept the API terms.
3. Name the key (anything) and create it. You get a test key right away.
4. In the Better GIFs plugin settings, set "GIF provider" to KLIPY and paste the key into "KLIPY API key".

Test keys are limited to 100 calls an hour (KLIPY partner panel guide). That should be enough for normal use, since searches are debounced and cached for 10 minutes. Heavy users can request a production key from the same panel.

Not tested against the live KLIPY API (no key available while writing this), so the response mapping follows KLIPY's docs. Worth a quick try with a real key before merging. If you'd rather host a keyless proxy, happy to rework it that way.

[Transparency: This PR was made entirely with AI, however was reviewed before by a human. As always, my AI commits will carry the AI ai@izie.top co-author. You can read more about my usage of AI at https://izie.top/usage]