refactor: completely deprecate and remove Ollama runtime in favor of embedded llama.cpp

[BerryUIKI]

Summary

• Completely removes all Ollama background supervisor, client calls, and endpoints (/api/v1/ollama/*).
• Replaces external runtime dependencies with embedded, zero-pollution llama.cpp (llama-server) and multi-mirror GGUF downloads.
• Cleaned up \SetupWizardModal\ and \SettingsView\ to remove Ollama banner, selectors, and state.
• All 157 backend tests passing, frontend TypeScript and Vite builds clean.