[krosct]

Problem

Battery threshold colors (battery-colors) only apply to Percentage. The Power Rate sensor (format watt), which is also the battery value shown in the top bar, never gets a color, because helpers/catalog.js lists only 'percent' in the battery colorFormats.

So:

• an "All sensors" color scale on the Battery page does not color Power Rate;
• if Power Rate is pinned to the panel, it is offered in the "Add Color Scale" dropdown and a scale can be saved for it, but that scale is never applied;
• if it is not pinned, it is not offered in the dropdown at all.

Changes

• helpers/catalog.js: add 'watt' to the battery colorFormats. Power Rate, including the battery value in the panel, now uses battery-colors: both the "All sensors" scale and a per-sensor scale are applied, and Power Rate is listed in "Add Color Scale" whether or not it is pinned.
• schemas/org.gnome.shell.extensions.vitals.gschema.xml: the battery-colors description now mentions power rate (watts). The key's type and default are unchanged, so existing settings keep working (scales already saved for Power Rate start to apply).

Notes

• Power Rate is matched in watts, with a sign: positive while charging, negative while discharging. Thresholds use the existing value >= threshold rule, so negative breakpoints can color discharge rates.
• Validated with glib-compile-schemas --strict --dry-run schemas/.
• Tested on GNOME Shell 50.1 (Wayland): Power Rate is colored by both an "All sensors" scale and a per-sensor scale.