fix(locksmith): block private URLs in OG/certification image fetch

[SashaMIT]

Why

Unauthenticated GET /v2/og/event/... (and certification) fetch lock metadata.image / event_cover_image through imageURLToDataURI with bare fetch and no scheme/private/redirect guard.

Distinct from #16593 (WebSub hub.callback) and #16594 (Apple Wallet thumbnail). Same SSRF class; this PR introduces the shared assertSafeCallbackUrl helper for the image path (sibling PRs add the same helper for their sinks — land one first and rebase the others if needed).

Fix

• Add assertSafeCallbackUrl (http(s) + DNS private/link-local/CGNAT block)
• Call it in imageURLToDataURI before fetch with redirect: 'error'

Test plan

• yarn vitest run __tests__/utils/image.test.ts __tests__/utils/safeCallbackUrl.test.ts (6/6)
• Public https lock images still render in OG
• http://127.0.0.1/... / metadata IP fail closed (fallback / throw)

Made with Cursor

[cla-bot]

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[SashaMIT]

Follow-up commit on this branch: the same unauthenticated SSRF class also sits on GET /image/:network/:lockAddress/:keyId (getTokenURIImage).

It bare-fetched key.tokenURI and redirected the client to json.image with no scheme/private/DNS/redirect guard. Now both URLs go through assertSafeCallbackUrl with redirect: 'error', consistent with the OG/Apple paths in this PR family.

[cla-bot]

Thank you for your pull request and welcome to Unlock! We require contributors to sign our Contributor License Agreement, and we don't seem to have the users @SashaMIT on file.
In order for us to review and merge your code, please open another pull request with a single modification: your github username added to the file .clabot.
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[SashaMIT]

CLA sign PR opened per cla-bot: #16596 (single-file .clabot add for SashaMIT). Once that merges, verification/cla-signed should clear on this PR. Vercel authorize remains maintainer-side.