Fix logging broken on 32-bit Linux systems with 64-bit time_t

[miketweaver]

Problem

On modern 32-bit Linux systems (Raspberry Pi with recent Debian/Raspbian),
the logging system produces corrupted log files with garbage filenames and
timestamps. The /jl API endpoint returns empty results even though log
files exist in the logs/ directory.

Root Cause

Since glibc 2.34, time_t is 64-bit on 32-bit systems to address the
year 2038 problem. The logging code passes time_os_t (which is time_t)
directly to snprintf with %lu format specifier, which expects 32-bit
unsigned long. This type mismatch causes undefined behavior.

Symptoms

• Log files created with incorrect names (e.g., 5212016.txt instead of 20420.txt)
• Timestamps in log entries are garbage values
• /jl?hist=7 API returns [] because expected filenames don't exist
• Issue manifests on 32-bit ARM Linux with glibc >= 2.34

Solution

Explicitly cast time_os_t values to unsigned long before passing to
snprintf with %lu:

// Before

snprintf(tmp_buffer, TMP_BUFFER_SIZE, "%lu", curr_time / 86400);

// After

snprintf(tmp_buffer, TMP_BUFFER_SIZE, "%lu", (unsigned long)(curr_time / 86400));

Tested on:

• Raspberry Pi (armv7l, 32-bit)
• Debian (dietpi) with glibc 2.41
• Confirmed log files now have correct day-based filenames
• Confirmed /jl API returns expected log entries

This should be tested on other devices to make sure it doesn't break it for those other devices. I only have this one raspberry pi so it's all I could test with.