Add DGrid Free Models Router provider

[ethanclarkeio]

Summary

Adds DGrid as an OpenAI-compatible provider and seeds the dgridai/free Free Models Router as a recurring-free model.

The DGrid Free Models Router provides a single free smart-routing endpoint over DGrid's current free model pool, with conservative default limits of 10 requests/minute and 100 requests/day. The README also documents the optional $5 lifetime top-up quota and briefly notes DGrid's broader 200+ model catalog.

Changes

• Register DGrid with the OpenAI-compatible provider registry
• Add dgrid to platform types, key creation, and the Keys page provider list
• Seed dgridai/free with free-tier limits and fallback config
• Document DGrid Free Models Router in the README
• Add provider, key route, and migration coverage

Verification

• npm run build
• npm test

[tashfeenahmed]

Thanks. The provider registration part is fine, but model rows can't ship as DB migrations anymore: model data is owned by the hosted catalog now, and this also currently conflicts on migrations. Could you re-cut with just the provider plumbing? Separately, before wiring a third-party aggregator in, I'd want some signal on DGrid's stability and terms; if you have links to their docs/ToS, drop them here.

[tashfeenahmed]

Thanks for the provider work. One policy thing blocks this in its current shape: model and catalog rows must not ship as migrations. The catalog is delivered by the published catalog service, which is also where tier gating happens, so seeding those rows in a migration puts them outside that path and they end up diverging from what the service publishes. That's what the comment in migrations.ts is there to prevent, so it needs to stay as-is rather than be rewritten.

Happy to take the rest, though. If you drop the migration and the comment rewrite and keep the provider plumbing — the registry entry, PLATFORMS, the KeysPage changes, and the tests — I can merge it after a rebase on current main.