docs(local-llm): add multimodal stack, model recommendations, and troubleshooting
- docs/04-multimodal-local-stack.md: vision models (llava, qwen2.5vl, moondream2),
audio pipeline architecture, video understanding status, Kimi alternatives,
complete local AI stack diagram
- docs/07-model-recommendations.md: 6-tier model guide (coding, fast, general,
reasoning, vision, embeddings), recommended 10-model stack for M4 Pro 48GB,
use-case quick reference, hardware scaling guide
- docs/08-troubleshooting.md: corporate Forcepoint proxy workarounds, MLX warning,
JSON parse errors, slow inference, whisper-cli vs whisper-cpp naming, audio
format conversion, proxy-corrupted downloads detection
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