fix: resolve stat command multi-line output breaking verify command

The stat command was producing multi-line output which broke the pipe-delimited
return format of verify_model_download(). Fixed by:
- Testing which stat format works (Linux vs macOS) before executing
- Using proper format flags to get single-line date output
- Defaulting to 'Unknown' instead of relying on fallback chain

This fixes the issue where all models showed as 'NOT DOWNLOADED' even when
present in the cache.

artifact_huggingface_download.sh

@@ -638,18 +638,11 @@ verify_model_download() {
     local expected_size_gb="$2"
     local filename_filter="$3"
 
-    # DEBUG: Show what we're checking
-    echo "DEBUG_BASH: Checking repo_id='$repo_id' filter='$filename_filter' CACHE_DIR='$CACHE_DIR'" >&2
-
     # Find model files in cache
     # Capture both stdout (file paths) and stderr (error messages)
     local find_output
     find_output=$(find_model_files "$repo_id" "$filename_filter" 2>&1)
 
-    # DEBUG: Show raw output
-    echo "DEBUG_BASH: find_output length=${#find_output}" >&2
-    echo "DEBUG_BASH: find_output first 200 chars: ${find_output:0:200}" >&2
-
     # Separate file paths from error/debug messages
     local model_files
     model_files=$(echo "$find_output" | grep -v "^ERROR:" | grep -v "^WARN:" | grep -v "^DEBUG:")
@@ -680,13 +673,17 @@ verify_model_download() {
     cache_path=$(echo "$model_files" | head -n1 | xargs dirname)
 
     # Get modification time of first file
-    local mod_time=""
+    local mod_time="Unknown"
     if [[ -n "$model_files" ]]; then
         local first_file
         first_file=$(echo "$model_files" | head -n1)
         if [[ -f "$first_file" ]]; then
-            mod_time=$(stat -f "%Sm" -t "%Y-%m-%d %H:%M:%S" "$first_file" 2>/dev/null || \
-                       stat -c "%y" "$first_file" 2>/dev/null | cut -d'.' -f1 || echo "Unknown")
+            # Try Linux stat first (most common), then macOS stat
+            if stat -c "%y" "$first_file" >/dev/null 2>&1; then
+                mod_time=$(stat -c "%y" "$first_file" 2>/dev/null | cut -d'.' -f1)
+            elif stat -f "%Sm" "$first_file" >/dev/null 2>&1; then
+                mod_time=$(stat -f "%Sm" -t "%Y-%m-%d %H:%M:%S" "$first_file" 2>/dev/null)
+            fi
         fi
     fi