fix(theme): restore used-disk base on the storage gauge in dark theme

In dark theme chart_track (the 'used disk' segment) was #333333 — identical to
dash_bar_bg (the background arc) — so the used-disk base vanished and the gauge
looked like a dot floating with no base. Set it to a light near-white (#E8EAED)
so the base reads clearly on the dark arc, matching the previous version. Light
theme keeps its existing #C4C7CC.

Author: luisguzman-adfa

controller/app/src/main/res/values-night/colors.xml

@@ -40,7 +40,7 @@
     <color name="chart_os">#26C6DA</color>
     <color name="chart_maps">#FF9800</color>
     <color name="chart_wiki">#66BB6A</color>
-    <color name="chart_track">#333333</color>
+    <color name="chart_track">#E8EAED</color>
     <!-- Round 2 (Usage/Install/Share migration) — twins of values/colors.xml -->
     <color name="surface_active_success">#173317</color>
     <color name="surface_active_info">#17263A</color>