refactor: separate log output to stdout and file, gracefully handling file write failures.

demo/capture-upload.sh

@@ -45,7 +45,9 @@ RETRY_DELAY="${RETRY_DELAY:-5}"
 log() {
     local timestamp
     timestamp=$(date '+%Y-%m-%d %H:%M:%S')
-    echo "[$timestamp] $*" | tee -a "$LOG_FILE" 2>/dev/null || echo "[$timestamp] $*"
+    local msg="[$timestamp] $*"
+    echo "$msg"
+    echo "$msg" >> "$LOG_FILE" 2>/dev/null || true
 }
 
 log_error() {