[FR] - Add OrcaRouter as a built-in AI provider #1196

Is your feature request related to a problem? Please describe.
WhoDB's AI chat assistant currently has one OpenAI-compatible gateway-style provider gap: users who want to pick from many models behind a single API key (OpenAI, Anthropic, Google, DeepSeek, Qwen, MiniMax, xAI) must either add OrcaRouter as a generic WHODB_AI_GENERIC_* provider or skip it. A first-class provider entry would make it a one-token setup like OpenAI or Anthropic.

Describe the solution you'd like
Add OrcaRouter as a built-in AI provider in the Chat configuration, following the same pattern as the existing OpenAI/Anthropic built-ins:

• A registered OrcaRouter provider type in the Go provider registry, backed by the OpenAI-compatible adapter, defaulting to https://api.orcarouter.ai/v1.
• Environment variables WHODB_ORCAROUTER_API_KEY, WHODB_ORCAROUTER_ENDPOINT, and WHODB_ORCAROUTER_NAME so server-side deployments can preconfigure it (mirroring WHODB_OPENAI_*).
• A frontend catalog entry and icon so the provider renders with its label and logo in the AI Provider dropdown, including the "Add a provider" flow.
• Docs section and env-var reference in docs/ai/setup-providers.mdx.

Describe alternatives you've considered

• Generic WHODB_AI_GENERIC_ORCAROUTER_* env vars already work today, but they are invisible in the built-in catalog and require users to know the exact model list. A named provider keeps the model picker live (models are fetched from /models) and matches how OpenAI/Anthropic are handled.
• OpenRouter-style third-party integration is out of scope; this is specifically about the OrcaRouter gateway.

Additional context
OrcaRouter is an OpenAI-compatible model routing gateway. Its model names use a provider/model format (e.g. openai/gpt-5.5, anthropic/claude-sonnet-4.6, orcarouter/auto), so model discovery via /v1/models works with the existing OpenAI-compatible adapter unchanged.