feat(memory_manager): add OrcaRouter as a named memory-manager backend

[XiaoHuo888-hue]

Add OrcaRouter as a named memory-manager backend

OrcaRouter is an OpenAI-compatible LLM gateway (API base https://api.orcarouter.ai/v1, keys prefixed sk-orca-). It also runs gateway-level, zero-trust security for AI agents on the same endpoint — screening every prompt/response and governing every tool call on a default-deny basis, with no application code changes.

This PR registers OrcaRouter as a first-class named backend for MemoryManagerConfig, mirroring the existing DeepSeek provider — so users can select it via model_name: "orcarouter" instead of manually pointing a generic OpenAI-compatible endpoint.

Changes

• src/lightmem/configs/memory_manager/base_config.py: add orcarouter_base_url config slot (defaults to https://api.orcarouter.ai/v1)
• src/lightmem/configs/memory_manager/base.py: register orcarouter in MemoryManagerConfig._model_list
• src/lightmem/factory/memory_manager/orcarouter.py: new OrcaRouterManager (subclasses DeepseekManager; OpenAI client, default model orcarouter/auto, key from ORCAROUTER_API_KEY or config.api_key)
• src/lightmem/factory/memory_manager/factory.py: map orcarouter → OrcaRouterManager
• tests/test_orcarouter.py: unit tests for config acceptance, factory instantiation, defaults, custom base URL, and missing-key error
• README.md: news entry + supported-backends table + config example

Example

"memory_manager": {
    "model_name": "orcarouter",
    "configs": {
        "model": "orcarouter/auto",
        "api_key": "sk-orca-...",
        "orcarouter_base_url": "https://api.orcarouter.ai/v1"
    }
}

Validation

• pytest tests/ — 7 passed (2 existing + 5 new)
• flake8 / isort clean on new files; py_compile OK
• Live test against the real OrcaRouter endpoint through the new OrcaRouterManager path returned ORCA-LIVE-OK with valid token usage (HTTP 200)

Disclosure: I'm an engineer on the OrcaRouter team.