Pad the percent text to 3 chars with printf so " 5%", " 50%", and
"100%" render at identical width in the JetBrainsMono monospace label.
Previously the popup container resized between events because the
label string varied between 2 and 4 characters, which caused the
popup to visibly jump in width on consecutive brightness key presses.
Builds on #5525, which made the percent values themselves step
uniformly; this completes the loop by making the rendered popup match.
Co-authored-by: Mateus Pegorim <14262063+Pegorim@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
