fix(distributed): self-heal stale 'model not loaded' routing

[localai-bot]

Problem

In distributed mode a model can become unreachable with <backend>: model not loaded and stay broken until the controller is restarted.

Sequence:

1. A model is loaded on a worker; the registry records it as loaded on that node.
2. The worker evicts the model (autonomous LRU eviction, an out-of-band unload, memory pressure) but the backend process survives.
3. The registry still lists the model as loaded there.
4. On the next request, the router's cached-node check (SmartRouter.probeHealth) only verifies the process is alive — not that the model is loaded — so it routes to that node.
5. The inference call returns model not loaded. The stale registry row is never cleared, so every subsequent request keeps routing back to the same evicted node.

A controller restart "fixes" it only because it rebuilds the registry from scratch.

Observed live with a realtime pipeline: parakeet-cpp: model not loaded returned instantly with no staging/load attempt on the worker, persisting until the controller was restarted (after which the model re-staged and transcribed fine).

Fix

InFlightTrackingClient now self-heals: when a tracked inference call returns a model-not-loaded error, it drops the stale replica row via RemoveNodeModel, so the next request reloads the model on a healthy node instead of routing back to the evicted one. The original error is returned to the caller unchanged — only the registry is corrected.

• Applied to every tracked inference method (Predict, PredictStream, Embeddings, TTS, TTSStream, AudioTranscription, AudioTranscriptionStream, image/video/sound/detect/rerank).
• InFlightTracker gains RemoveNodeModel (already implemented by NodeRegistry).

This makes the failure transient and self-correcting (one failed request, then automatic recovery) instead of permanent-until-restart.

Tests

TDD — new specs in inflight_test.go: a model not loaded error drops the replica (for unary and streamed calls); an unrelated error and a success do not. Full core/services/nodes suite passes.