Parse a User-Agent string into browser, OS, device, and engine details using regex heuristics.
Parsing is done with heuristic pattern matching against known User-Agent formats. It covers the most common browsers, operating systems, and devices well, but User-Agent strings are not standardized and some combinations (spoofed, unusual, or very new UAs) may not be recognized accurately. Fields that can't be confidently determined are shown as "Unknown" rather than guessed.