fix: deduplicate OG image upserts

[KaannKara]

Fixes #287.

Summary

• deduplicate scraped OG images by URL before running batched upserts
• add a regression test for duplicate og:image URLs within the same origin

Tests

• pnpm --filter @x402scan/app test:run src/services/db/resources/origin.test.ts
• pnpm --dir apps/scan exec eslint src/services/db/resources/origin.test.ts --max-warnings 0
• pnpm --filter @x402scan/app format:check
• git diff --check

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