Cost intelligence panel and routing decision log

The admin console now breaks down spend per model with trend indicators and an estimated savings figure against an always-cheapest baseline. Every routing decision is recorded with the score each candidate model received, so operators can audit exactly why one provider was chosen over another and analyze distribution over time. Six admin pages gain CSV and JSON export, and all admin list endpoints are paginated server-side. Provider API keys are encrypted at rest with Fernet; an optional HashiCorp Vault backend is available for deployments that require key material to live outside the primary database.

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