[FEATURE] Support TrustedRouter as an OpenAI-compatible provider

Feature Area: Integration with external tools

Problem

NA — not related to an existing bug.

TrustedRouter is an OpenAI-compatible LLM router at https://api.trustedrouter.com/v1. CrewAI already routes several OpenAI-compatible gateways natively (OpenRouter and friends), but reaching TrustedRouter today means hand-setting base_url on every LLM, and the routing aliases do not survive the prefix strip that native routing applies.

Describe the solution you'd like

Register trustedrouter alongside the existing OpenAI-compatible entries:

• Runtime routing in crewai.llm.LLM so LLM(model="trustedrouter/auto") and LLM(model="trustedrouter/moonshotai/kimi-k3") both reach OpenAICompatibleCompletion, with TRUSTEDROUTER_API_KEY and an optional TRUSTEDROUTER_BASE_URL override.
• A trustedrouter/ section in the LLM concept guide (en, plus the ar, ko and pt-BR translations that carry the same provider list).

One detail worth calling out, because it is the part that is not a copy of the OpenRouter handling: every TrustedRouter model id is namespaced, so the prefix strip that is correct for OpenRouter breaks the router's own aliases — trustedrouter/auto reaches the API as auto, which it rejects. trustedrouter/moonshotai/kimi-k3 still has to resolve to the upstream id, so the split is on whether the remainder is left bare, not on the provider alone.

Describe alternatives you've considered

Configuring base_url per-LLM works today but leaves the aliases unusable and gives no CLI/docs discoverability, which is the same argument that applies to the gateways CrewAI already routes natively.

Additional context

Implementation is written and passing — ruff check clean, tests/llms/openai_compatible green (43) — in #6143, which was auto-closed for not referencing an issue. This is that issue.

Willingness to Contribute

Yes, I'd be happy to submit a pull request

Start in crewai.llm.LLM and compare the existing OpenAI-compatible provider routing. Review tests/llms/openai_compatible, where the issue reports 43 passing tests, then inspect the LLM concept guide in English and the ar, ko, and pt-BR translations. Done means TrustedRouter routing and its documented provider section are covered while the existing test suite remains green.