fix: avoid build-time root-owned cache env dirs

Dockerfile

@@ -2,16 +2,6 @@ FROM python:3.11-slim
 
 WORKDIR /app
 
-ENV HOME=/tmp/context-corruption-training \
-    XDG_CACHE_HOME=/tmp/context-corruption-training/cache \
-    HF_HOME=/tmp/context-corruption-training/cache/huggingface \
-    HF_HUB_CACHE=/tmp/context-corruption-training/cache/huggingface/hub \
-    TRANSFORMERS_CACHE=/tmp/context-corruption-training/cache/huggingface/transformers \
-    WANDB_DIR=/tmp/context-corruption-training/wandb \
-    WANDB_CACHE_DIR=/tmp/context-corruption-training/cache/wandb \
-    MPLCONFIGDIR=/tmp/context-corruption-training/cache/matplotlib \
-    OUTPUT_DIR=/tmp/context-corruption-training/checkpoints/grpo-qwen-1.5b
-
 RUN apt-get update && apt-get install -y git build-essential && rm -rf /var/lib/apt/lists/*
 
 # Stable cu121 torch — TorchAO import shims are applied at runtime before Unsloth loads.