fix: preserve Ollama status diagnostics (#6702)

[atomantic]

Summary

• preserve Ollama runtime, applied, and minimum context-window diagnostics in the public local-LLM status response
• expose Ollama model-list failures separately from a successful empty model list
• cover the public service boundary for populated and null runtime contexts and failed-versus-empty model discovery

Test plan

• cd server && npm test -- localLlm.test.js (136 tests)
• cd client && npm test -- LocalLlmRuntimesView.test.jsx LocalLlmLibraryView.test.jsx (64 tests)
• cd client && npm run lint

Closes #6702