fix: JS formatBytes unit index off-by-one for realtime updates

The JS formatBytes used floor(log1000(b)) directly as the units index,
but this returns a value 1 too high. For 642MB (642000000 bytes):
log1000 gives ~2.94 → floor 2 → units[2]='GB' (wrong, should be MB).

Root cause: Go formatBytes counts how many times b/1000 is still ≥ 1000
(loop condition n >= unit), which produces exp where divisor=1000^(exp+1).
But JS formula floor(log1000(b)) counts how many times b ≥ 1000^n
without the extra division check, making it off by 1.

Fix: separate exp (power of 1000) from i (units index), where i = exp-1
and divisor = 1000^exp. This mirrors the Go logic exactly.

Author: coderbuzz

internal/http/templates/live_charts.html

@@ -5,9 +5,10 @@
   b = Number(b);
   if (b < 1000) return Math.round(b) + ' B';
   var units = ['kB','MB','GB','TB','PB'];
-  var i = Math.floor(Math.log(b) / Math.log(1000));
+  var exp = Math.floor(Math.log(b) / Math.log(1000));
+  var i = exp - 1;
   if (i >= units.length) i = units.length - 1;
-  return (b / Math.pow(1000, i)).toFixed(1) + ' ' + units[i];
+  return (b / Math.pow(1000, exp)).toFixed(1) + ' ' + units[i];
 }
 
 // initLiveCharts wires up a live (1s) WebSocket chart + gauge feed for a server