fix(scaleway): support project-scoped keys and chat-completions endpoint

[albanm]

Fixes the Scaleway provider, which returned an empty model dropdown, and makes the failure that caused it visible instead of silent.

What changed

• Scaleway project-scoped keys: add an optional Project ID on the Scaleway provider. When set, requests target https://api.scaleway.ai/{projectId}/v1 instead of the bare /v1 (the org default project). A key scoped to a single Project returned 403 insufficient permissions against the bare URL, leaving the model dropdown empty.
• Scaleway chat endpoint: switch Scaleway inference to the .chat() model. The default @ai-sdk/openai v3 callable targets /v1/responses, which Scaleway does not implement (returns 422 ROUTE NOT SUPPORTED) — the same fix applied to openai-compatible in feat: add compatibility mode for openai-compatible providers #44.
• Surface model-listing errors: the per-provider fetchers no longer swallow errors and return []. GET /models now returns { results, count, errors }, and the admin settings page shows a warning naming each provider that failed and why. This is the diagnosability gap the Scaleway bug exposed — the 403 was only visible in server logs.

Why: a user reported "Scaleway is broken, it doesn't list its models." Root cause was the hardcoded default-project URL for a project-scoped key; the empty dropdown gave no hint why, which is what motivated the error-surfacing change.

Verified: unit tests for the URL helper; API tests proving a failing provider is reported while working providers still list; lint + type-check clean. Confirmed live against the Scaleway API: project-scoped /v1/models and /v1/chat/completions return 200, /v1/responses returns 422.

Heads-up for reviewers

• GET /models response gained an errors key (additive; the vjsf autocomplete reads results only).
• Listing results (incl. errors) are memoized 5 min keyed on updatedAt; saving settings busts the cache, so a fixed key reflects immediately.
• Most of the diff is regenerated build-types output (validate.js, vjsf-put-req-*.vue) — mechanical identifier renumbering from the one new schema field, no hand edits there.