feat: auto-download missing .so dependencies from ModelScope on Linux

Mirror the Windows dependency resolution for Linux: when the worker
fails to load libquantfunc.so due to missing shared libraries,
download cu1x-dep-linux.zip from ModelScope, extract to bin/linux/,
and retry with dll_dir in LD_LIBRARY_PATH.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>