fix(sglang): implement Status RPC to unblock backend-monitor polling

[pos-ei-don]

Problem

The sglang Python backend inherits the default Status RPC from backend_pb2_grpc.BackendServicer, which raises NotImplementedError. LocalAI's backend-monitor polls /backend.Backend/Status periodically on every registered backend; when the call fails, /backend/monitor returns HTTP 500 and downstream inference requests to the sglang backend get blocked — even though the model is loaded and answering fine on its direct gRPC endpoint.

Fix

Add a minimal Status shim that mirrors the existing Health method and returns StatusResponse{state=READY} unconditionally. This unblocks the monitor path immediately. A state-aware follow-up (UNINITIALIZED during load, BUSY under active inference) would be an improvement but is intentionally out of scope for this MVP — the current change matches what Health does today, which is what registered backends have effectively been telling the monitor loop anyway.

Reproducer / verification

Hardware: DGX Spark (GB10, arm64-l4t-cuda-13 image). Backend: cuda13-nvidia-l4t-arm64-sglang at sglang v0.5.15, model ucbye/Qwen3-Coder-Next-NVFP4-GB10 (80B NVFP4). Before the shim, /backend/monitor returns 500 and inference requests routed via LocalAI hang; direct gRPC-level calls to the sglang server work. Patching the shim in place on the running container instantly restores both /backend/monitor and inference to the sglang slot. Same pattern has been carrying prod for the sglang coder there since 2026-07-15 (~24 h uptime).

Notes for reviewers

• The change is 8 lines in backend/python/sglang/backend.py; nothing else is touched.
• Other Python backends (e.g. vllm, llama-cpp-python) also don't implement Status today — if the monitor polls them too, the same shim would apply. I've only reproduced the failure end-to-end with sglang so this PR is intentionally sglang-only; happy to file follow-ups if useful.
• Cross-ref: same pattern of "sglang wrapper missing a method that vllm has" as fix(sglang): parse tool_call function arguments before applying the chat template #10558 (function.arguments string→dict parse).

[localai-bot]

Reviewed against the codebase — the fix is correct and verified:

• core/services/monitoring/backend_monitor.go:93 does poll Status on every registered backend, and the sglang servicer indeed inherits the unimplemented default, so the failure mode described (500 on /backend/monitor for a healthy loaded model) is real.
• The shim matches the established pattern in other Python backends (speaker-recognition, insightface, rfdetr all implement the same minimal Status).
• Unconditional READY is the right call here rather than a state-aware variant: self.llm only exists after LoadModel, and the monitor only samples models that already passed CheckIsLoaded, so Health-mirroring behavior is consistent.

One blocker before merge: the DCO check is failing — please amend your commit with a Signed-off-by line (git commit --amend -s and force-push). Cosmetic nit, feel free to ignore: there's a double blank line before Status and none between it and LoadModel.

cc @mudler — good to merge once DCO is fixed.