feat(llm): wire list_models_remote into AnyProvider, RouterProvider, ModelOrchestrator

[bug-ops]

Parent Epic

#991

Depends On

#992 #993 #994 #995

Summary

Propagate list_models_remote through the dispatcher layer so callers always
get the full model list regardless of which AnyProvider variant is active.

Changes

AnyProvider

Add delegation via the existing delegate_provider! macro:

// any.rs
impl LlmProvider for AnyProvider {
    async fn list_models_remote(&self) -> Result<Vec<ModelInfo>, LlmError> {
        delegate_provider!(self, |p| p.list_models_remote().await)
    }
}

RouterProvider

Aggregate models from all fallback providers, deduplicating by id:

async fn list_models_remote(&self) -> Result<Vec<ModelInfo>, LlmError> {
    let mut seen = std::collections::HashSet::new();
    let mut result = Vec::new();
    for provider in &self.providers {
        if let Ok(models) = provider.list_models_remote().await {
            for m in models {
                if seen.insert(m.id.clone()) {
                    result.push(m);
                }
            }
        }
    }
    Ok(result)
}

ModelOrchestrator

Aggregate across all registered sub-providers, tagging each ModelInfo
with the sub-provider name in display_name prefix when ambiguous:

async fn list_models_remote(&self) -> Result<Vec<ModelInfo>, LlmError> {
    // iterate self.providers (HashMap<String, SubProvider>)
    // collect and deduplicate
}

Acceptance Criteria

• AnyProvider::list_models_remote delegates to inner variant.
• RouterProvider returns union of all providers, no duplicates.
• ModelOrchestrator returns union of all sub-providers.
• All existing unit tests pass.
• Integration test: AnyProvider::Ollama → list_models_remote hits mock Ollama.