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 -->

Cargo.toml

@@ -53,7 +53,7 @@ resolver = "3"
   libc = "0.2"
   libwebp-sys = "0.14.2"
   little_exif = "0.6.23"
-  llm_adapter = { version = "0.1.3", default-features = false }
+  llm_adapter = { version = "0.1.4", default-features = false }
   log = "0.4"
   loom = { version = "0.7", features = ["checkpoint"] }
   lru = "0.16"