Register AgentRouter across the provider registry, pricing, docs, and
dashboard metadata so it appears as a first-class OpenAI-compatible
passthrough option.
Add a dedicated `/api/models/test` endpoint and provider-page controls
for on-demand single-model diagnostics, including latency feedback and
success/error status, to help verify mappings without triggering broader
connection tests or rate limits.
Align header casing expectations in provider validation tests with the
current registry contract.
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