Add Fireworks fallback for CanopyWave

[jahooma]

Adds a server-side fallback from CanopyWave to Fireworks for supported models when CanopyWave returns availability failures such as 429, 5xx, or "No available workers".
If CanopyWave is not configured, supported models now route directly to Fireworks instead of failing on the missing key.
This keeps the existing provider billing/logging paths intact and covers both streaming and non-streaming completions.
Validated with bun test web/src/app/api/v1/chat/completions/__tests__/completions.test.ts and bun run --cwd web typecheck.

Your free trial has ended. If you'd like to continue receiving code reviews, you can add a payment method here.

This PR modifies files under web/src/app/api/v1/chat/completions/_post.ts and its test file, which fall under the web/ path excluded from this mirror's review scope per repo policy. Regardless of the change's technical merit (the CanopyWave→Fireworks fallback logic and the added test coverage for both streaming and non-streaming paths look reasonable and well-tested), this repo cannot accept changes to web/. If this is meant to be ported to the private tree, it should go through that internal process rather than this mirror.

PR checks failed

A couple of things need fixing before this can be reviewed.
None of them are about the code itself.

This PR touches paths the public mirror does not accept.

• web/src/app/api/v1/chat/completions/__tests__/completions.test.ts
• web/src/app/api/v1/chat/completions/_post.ts

Backend, database, billing and deployment code is not part of
this repository. A change to those paths cannot be merged here
regardless of its quality. See CONTRIBUTING.md for the paths
that are in scope.

---

Edit the PR and this check re-runs automatically.