fix: handle OgImage unique constraint conflict for shared URLs across origins

[artylobos]

Summary

Fixes #287

Problem

When registering a new resource, registration fails with a database unique constraint error if two different origins share the same OG image URL (e.g., via shared CDN or redirect).

Root Cause

1. Within a single origin: Duplicate og:image tags with the same URL cause parallel upserts with the same composite key, creating a race condition.
2. Across origins: If migration 20260115100000 hasn't been applied in production, a legacy unique index on OgImage.url still exists, causing P2002 errors when a URL is already stored under another origin.

Fix

• Deduplicate OG images by URL within each origin before upsert (prevents race condition from duplicate tags)
• Wrap upsert in try/catch for Prisma P2002 unique violation
• Gracefully skip if OgImage URL already exists for another origin (no data loss - the image is already stored)

Changes

Modified apps/scan/src/services/db/resources/origin.ts:

• Deduplicate ogImages by URL using Map before upsert
• Wrap each ogImage upsert in try/catch
• Handle P2002 Prisma error code for legacy url unique constraint
• Skip silently when image URL exists under another origin

Testing

This fix handles both scenarios described in #287:

1. Multiple origins sharing the same OG image URL
2. Duplicate og:image tags within a single origin's scraped metadata

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