Enhance tooltip functionality for CPU standard deviation in dashboard

- Updated the tooltip for the CPU standard deviation metric to include a detailed explanation of the calculation, preserving newlines for better readability.
- Added CSS styles to support multi-line tooltips, improving user comprehension of the displayed data.

static/css/main.css

@@ -340,4 +340,10 @@ label.swap:focus-within:not(.theme-toggle) {
   .print-only {
     display: none !important;
   }
+}
+
+/* Multi-line tooltip (formula): preserve newlines from data-tip */
+.tooltip-formula[data-tip]::before {
+  white-space: pre-line;
+  text-align: left;
 }