Fix mojibake in /path loss budget gaseous label

HEEx attribute value syntax (label="...") treats the content as a
raw attribute string, not as an Elixir string literal — so escape
sequences like \u2082 are NOT interpreted and show up verbatim in
the rendered page. Replace with the literal subscript-2 characters
so the label reads 'Gaseous (O₂+H₂O)'.

lib/microwaveprop_web/live/path_live.ex

@@ -678,7 +678,7 @@ defmodule MicrowavepropWeb.PathLive do
         <div class="space-y-1 text-sm">
           <.budget_row label="FSPL (free-space)" value={@result.loss_budget.fspl} unit="dB" />
           <.budget_row
-            label="Gaseous (O\u2082+H\u2082O)"
+            label="Gaseous (O₂+H₂O)"
             value={Float.round(@result.loss_budget.o2 + @result.loss_budget.h2o, 2)}
             unit="dB"
           />