The Grid instruments are not selectable, though their metadata already ships in the canonical registry

### Problem

Goose users who buy inference on [The Grid](https://thegrid.ai) have to hand-write a custom provider config to use it, even though Goose already carries the metadata needed to support it.

The Grid is a spot market for inference: an id names a market instrument — a task type (`text`, `code`, `agent`) paired with a quality tier (`standard`, `prime`, `max`), plus lab-scoped markets — rather than a fixed model. Each request is filled by whichever supplier is competitive at the time.

**Disclosure:** I work on The Grid, so this is a self-listing. Flagging that rather than leaving it to be discovered.

### Why this one is unusually cheap for Goose

`the-grid-ai` is **already in the canonical registry in-tree** — `crates/goose-provider-types/src/canonical/data/provider_metadata.json` plus nine instruments in `canonical_models.json`, regenerated from models.dev. So context limits, tool-call flags and model ordering already resolve; what's missing is only the provider entry that makes them selectable.

That also means this needs no `skip_canonical_filtering`, unlike most community providers.

### Verification plan

- `cargo test -p goose-providers --lib declarative` — `expose_declarative_providers_enumerates_all_bundled_json_files` and `all_bundled_providers_are_valid` both cover a new definition
- `cargo test -p goose-provider-types --lib` for the canonical name resolution
- a live call against the endpoint to confirm chat and streaming, which I can run and paste

### Note on ordering

I have a candidate implementation up at #11876. I opened it before reading the Ready-issue rule in CONTRIBUTING, which was my mistake — I'm filing this so the problem can be discussed properly, and I'm happy for the PR to sit closed or in draft until this issue reaches Ready, or to be discarded entirely if you'd rather shape the solution differently.