feat(embeddings): add OpenRouter provider

[mameikagou]

Summary

• add OpenRouter as a named embedding provider in the TypeScript and Python SDKs
• support single and batched requests through https://openrouter.ai/api/v1/embeddings
• expose provider configuration in Docker Compose, the dashboard, model defaults, and documentation
• mask both OpenRouter API-key environment variables in the settings response
• batch query embeddings for all providers that already advertise simple-mode batch support

Configuration

OM_EMBEDDINGS=openrouter
OPENROUTER_API_KEY=sk-or-v1-...
OM_OPENROUTER_EMBEDDING_MODEL=openai/text-embedding-3-small

The default embedding model follows OpenRouter's official embeddings example. Users can select any compatible model through OM_OPENROUTER_EMBEDDING_MODEL.

Official API documentation: https://openrouter.ai/docs/client-sdks/typescript/api-reference/embeddings

Verification

• TypeScript: 10 test files, 52 tests passed
• TypeScript typecheck passed
• Python OpenRouter adapter: 4 tests passed

[nullure]

LGTM