feat: enable full liter-llm configuration

[clashofphish]

What is the proposed feature?

The current implementation of liter-llm has support for AWS Bedrock, but this is not turned on within xberg. Here is the summary of what I have found regarding this request.

Summary

The vlm OCR backend with a bedrock/... model (e.g. bedrock/amazon.nova-pro-v1:0) always fails, regardless of AWS credentials:
Error: OCR error: VLM OCR request failed: model=bedrock/amazon.nova-pro-v1:0, language=eng, image_size=998KB: authentication failed: {"Message":"Authorization header is missing"}

Tried static keys and a fresh SSO session exported via aws configure export-credentials — same error either way. The request reaches AWS with no Authorization header at all, so this isn't a credentials issue; SigV4 signing simply isn't compiled into the binary.

##Root cause

liter-llm's BedrockProvider only signs requests when built with its own bedrock feature (crates/liter-llm/Cargo.toml:47). Without it, signing_headers() (bedrock.rs:598-609) takes the #[cfg(not(feature = "bedrock"))] branch and returns an empty header vector, and auth_header() always returns None for Bedrock — so the request goes out unsigned.

xberg's crates/xberg/Cargo.toml pins liter-llm with features = ["native-http"] only, on every target (non-Windows: line 1098, Windows: line 1130, wasm32: line 1206) — bedrock is never requested. xberg exposes no feature of its own to opt in, and publish.yaml CI never adds it either, so every prebuilt @xberg-io/xberg-* binary ships with Bedrock signing compiled out.

This looks like a pure packaging gap, not an app-level bug — vlm_ocr.rs/client.rs build a generic request and hand it to liter_llm::DefaultClient with no Bedrock-specific logic of their own.

Reproduction

import { extract } from "@xberg-io/xberg";

await extract(
  { kind: "uri", uri: "some.pdf" },
  { ocr: { enabled: true, backend: "vlm", language: ["eng"], forceOcr: true,
           vlmConfig: { model: "bedrock/amazon.nova-pro-v1:0" } } },
);

With AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY/AWS_SESSION_TOKEN correctly exported.

Expected: signed SigV4 request, Bedrock returns a completion.
Actual: {"Message":"Authorization header is missing"}, independent of credential validity.

Environment

@xberg-io/xberg 1.0.11 (pins liter-llm 1.13.0) — same gating confirmed present in both latest releases
macOS, @xberg-io/xberg-darwin-arm64, Node v22

Why would this be a good addition?

The support for AWS Bedrock already exists in liter-llm. It just needs to be turned on for xberg. I have already confirmed this works locally by enabling it myself.