docs: Add math section to syntax reference + improve example comments

- five-syntax-en/ko: Add Math comparison table (Harbour RTL vs Go math)
- go_math_compare.prg: Detailed English comments explaining each section
- Example lists updated with go_math_compare.prg

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/go_math_compare.prg

@@ -1,12 +1,25 @@
-// Five Math Comparison: Harbour RTL vs Go math package
+// Five Math Comparison: Harbour RTL vs Go math Package
 //
-// Five has BOTH:
-//   1. Harbour built-in: Abs(), Sqrt(), Round(), Int(), Max(), Min(), Log(), Exp(), Mod()
-//   2. Go math package: math.Sqrt(), math.Sin(), math.Cos(), math.Pow(), math.Pi, ...
+// Five gives you BOTH math systems in ONE file:
 //
-// Harbour RTL = simple, familiar.
-// Go math    = complete, IEEE 754 precise, 60+ functions.
-// Five       = use BOTH in the same PRG file!
+//   Harbour RTL (9 functions):
+//     Abs(), Sqrt(), Round(), Int(), Max(), Min(), Log(), Exp(), Mod()
+//     - Familiar to every xBase developer
+//     - No IMPORT needed, always available
+//     - Perfect for business calculations
+//
+//   Go math package (60+ functions):
+//     math.Sin(), math.Cos(), math.Pow(), math.Pi, math.Hypot(), ...
+//     - Full IEEE 754 precision
+//     - Trigonometry, statistics, special values
+//     - Just add IMPORT "math"
+//
+// Why this matters:
+//   - Daily work: use Harbour RTL (shorter, simpler)
+//   - Scientific/financial: use Go math (complete, precise)
+//   - Mix both freely in the same function!
+//
+// This example compares them side-by-side and shows combined usage.
 
 IMPORT "math"