feat: explore profile chart + Gaussian stats (xc/yc/fwhm/amp/bkg)
Adds cv-profile canvas and explore-stats aside to _mini(); new explore-stats.js draws column/row projection profiles (info/warning colors) and estimates centroid, FWHM, peak and background analytically from the tile float32 data. Also fixes centerIndex in _renderExploreTile (was pointing to row-start instead of tile centre). Co-Authored-By:Claude Sonnet 4.6 <noreply@anthropic.com> Source Commit: 4383bd62 [skip ci]