feat: adapt cloudflare worker ai (#14732)

#### PR Dependency Tree


* **PR #14732** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Cloudflare Workers AI added as a Copilot provider (configurable in
admin settings).
  * Gemini 3.1 Flash Lite Preview model made available.

* **Behavior Changes**
* Reranking now uses a different default model identifier (affects
relevancy scores).

* **Tests**
* Rerank tests adjusted to focus on the updated model and expected
results.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.docker/selfhost/schema.json

@@ -1005,6 +1005,14 @@
             "baseURL": "https://api.openai.com/v1"
           }
         },
+        "providers.cloudflareWorkersAi": {
+          "type": "object",
+          "description": "The config for the Cloudflare Workers AI provider.\n@default {\"apiToken\":\"\",\"accountId\":\"\"}",
+          "default": {
+            "apiToken": "",
+            "accountId": ""
+          }
+        },
         "providers.fal": {
           "type": "object",
           "description": "The config for the fal provider.\n@default {\"apiKey\":\"\"}",