feat: add OpenRouter LLM and embedding support

[nanxingw]

Summary

• Add OpenRouterClient (inherits OpenAIClient) that skips convert_to_structured_output — non-OpenAI models (Anthropic, Gemini) routed through OpenRouter do not support strict mode / additionalProperties
• Add OpenRouterEmbedding (inherits EmbeddingEndpoint) with Bearer auth header for OpenRouter's embedding API
• Register "openrouter" as a new model_endpoint_type / embedding_endpoint_type in schemas and LLMClient factory

Files changed

• mirix/llm_api/openrouter_client.py — new LLM client
• mirix/embeddings.py — new embedding client + registration
• mirix/llm_api/llm_client.py — factory registration
• mirix/schemas/llm_config.py — schema Literal
• mirix/schemas/embedding_config.py — schema Literal
• tests/test_openrouter.py — 14 unit tests

Usage

llm_config:
  model: "anthropic/claude-haiku-4.5"
  model_endpoint_type: "openrouter"
  api_key: your-api-key
  model_endpoint: "https://openrouter.ai/api/v1"
  context_window: 128000

embedding_config:
  embedding_model: "google/gemini-embedding-001"
  embedding_endpoint_type: "openrouter"
  api_key: your-api-key
  embedding_endpoint: "https://openrouter.ai/api/v1"
  embedding_dim: 3072

Test plan

• 14 unit tests covering schema validation, factory, tool schema (no strict), tool_choice, force_tool_call, embedding auth, error handling, and OpenAI regression
• Smoke test: successfully created and searched 7 memories via OpenRouter
• LoCoMo eval: 69.1% accuracy (105/152) with Claude Haiku via OpenRouter

🤖 Generated with Claude Code

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