Fix: Use official HF Spaces preload_from_hub for model caching

Root cause: /data directory not accessible during Docker build
Solution: Use HF Spaces preload_from_hub feature (official best practice)

Changes:
- README.md: Add preload_from_hub configuration for both model repos
- README.md: Change cache paths from /data to ~/.cache/huggingface
- Dockerfile: Update HF cache environment variables to use ~/.cache
- Dockerfile: Remove failed /data download block (lines 100-120)
- code/demo.py: Keep local_files_only=True (already done)
- code/clip_retrieval.py: Keep local_files_only=True (already done)

This follows HF Spaces official documentation and fixes:
✅ Permission error during build
✅ Startup hang from runtime downloads

Updated: README.md

README.md

@@ -7,10 +7,13 @@ sdk: docker
 app_port: 7860
 pinned: false
 license: mit
+preload_from_hub:
+  - 0xZohar/object-assembler-models
+  - openai/clip-vit-base-patch32
 env:
-  HF_HOME: /data/.huggingface
-  HF_HUB_CACHE: /data/.huggingface/hub
-  TRANSFORMERS_CACHE: /data/.huggingface/transformers
+  HF_HOME: /home/user/.cache/huggingface
+  HF_HUB_CACHE: /home/user/.cache/huggingface/hub
+  TRANSFORMERS_CACHE: /home/user/.cache/huggingface/transformers
   HF_HUB_DISABLE_XET: "1"
   LDRAW_LIBRARY_PATH: /home/user/ldraw
 ---