fix(docs): avoid mdx/ssg runtime error in energy-tax formula

Replace the inline KaTeX block in the Energy Price & Tax Breakdown
section with a plain inline equation string.

The previous expression caused a Docusaurus SSG runtime failure on the
sensors page (ReferenceError during static rendering).

Impact: User docs build now succeeds consistently for the sensors page.

docs/user/docs/sensors.md

@@ -470,7 +470,7 @@ All min/max sensors include:
 
 Many price sensors expose the **raw energy price** (spot price) and the **tax component** as additional attributes. These are sourced directly from the Tibber API's `energy` and `tax` fields, which together make up the `total` price you see in the sensor state:
 
-$$\text{total} = \text{energy} + \text{tax}$$
+`total = energy + tax`
 
 ### Where These Attributes Appear