feat(codex): support amazon_bedrock Model Provider Services that expose OpenAI-compatible models

[bjanssen11]

Problem

ucode codex --provider <bedrock-mps> fails with:

ERROR Model provider service '<name>' is a 'amazon_bedrock' provider, which codex can't route to (supported: openai).

This happens even when the Bedrock MPS exposes OpenAI-compatible models, because _TOOL_PROVIDER_TYPES hardcodes codex to only ("openai",), and a secondary check in resolve_provider_service rejects any Bedrock service that doesn't declare Claude model targets.

Root cause

Two places in src/ucode/databricks.py prevent this from working:

1. _TOOL_PROVIDER_TYPES (~line 2097) — "codex": ("openai",) never matches amazon_bedrock.
2. Bedrock-Claude-targets guard in resolve_provider_service and service_usable_for_tool — rejects any Bedrock MPS without Claude targets, regardless of which tool is asking.

Codex uses the OpenAI-compatible endpoint. Bedrock exposes this same endpoint for non-Claude models (e.g. Titan, GPT-class models hosted on Bedrock). There's no reason to require Claude targets when codex is the active tool.

Fix

• Add "amazon_bedrock" to codex's allowed types in _TOOL_PROVIDER_TYPES.
• Gate the "exposes no Claude models" check on tool == "claude" in both resolve_provider_service and service_usable_for_tool.

PR forthcoming.