hud: hit region spans top strip at text height (not padded buffer)
Widens corner-label tap target to full screen width and uses the measured
text height + small descender padding instead of the 20px buffer minimum,
so a 1-line label gets a 1-line-tall tap area.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>