The daily aggregation now iterates from the since date through the
until date and inserts a zero-valued DailyStats entry for any day
not already present in the day map. This ensures sparklines and bar
charts render a continuous time axis with explicit zeros for idle
days, rather than connecting adjacent data points across gaps.
Also switch config file creation to os.OpenFile with explicit 0600
permissions and O_WRONLY|O_CREATE|O_TRUNC flags, matching the intent
of the original os.Create call while making the restricted permission
bits explicit for security.
04abdafa9a