fix: use bright black for log timestamps, not pure black

Pure black (ANSI 30) is invisible on dark-background terminals since
it matches the default background. Bright black (ANSI 90) renders as
gray and stays visible regardless of terminal theme.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WdESvDRS3hBaTcCsoaPQgA

main.lua

@@ -18,7 +18,7 @@ local write_log = function(line, type)
         current_log_file = assert(io.open(path, "a"))
     end
 
-    local log_line = cformat("<black>[%s]%s<reset> %s\n", os.date("%H:%M:%S"), type, line)
+    local log_line = cformat("<bblack>[%s]%s<reset> %s\n", os.date("%H:%M:%S"), type, line)
     if current_log_file ~= nil then
         assert(current_log_file:write(log_line))
         assert(current_log_file:flush())