feat(fitness): tinted body-part icons with semantic accents

Unifies PNG and SVG body-part images behind a single CSS-mask
render path, so both now colorize with a --accent CSS variable.
Accent splits by measurement type: --blue for proportion parts
(chest, shoulders, waist, hips) and --nord8 for muscle parts
(neck, biceps, forearms, thighs, calves). Stats cards gain a
matching 8%-tint fill and accent-colored hover border. History
page header image enlarged. Thigh SVG stroke-width bumped to 11
for better mask legibility.

static/fitness/measure/thigh.svg

@@ -5,7 +5,7 @@
    viewBox="0 0 230.97847 161.57938"
    version="1.1"
    xmlns="http://www.w3.org/2000/svg">
-  <g transform="translate(10.583333,-67.733332)" fill="none" stroke="currentColor" stroke-width="7.9375" stroke-linecap="round" stroke-linejoin="round">
+  <g transform="translate(10.583333,-67.733332)" fill="none" stroke="currentColor" stroke-width="11" stroke-linecap="round" stroke-linejoin="round">
     <path d="m -5.2938776,75.349546 c 0,0 37.0210826,-4.638254 65.9220826,-3.451251 16.254828,0.667607 16.716356,0.857996 37.092959,6.092661 20.583856,5.287909 30.187556,12.829711 52.828226,19.244569 22.64067,6.414855 47.35673,7.358215 58.11105,22.263325 10.75432,14.90511 4.33946,48.11142 4.33946,48.11142 0,0 4.7168,25.47075 3.01875,35.47038 -1.69804,9.99963 -4.7168,22.26332 -4.7168,22.26332" />
     <path d="m -6.6145834,170.25168 c 0,0 19.8105854,15.09378 43.2059404,17.73519 23.395358,2.64141 79.431013,-10.1883 95.090803,-13.39573 15.6598,-3.20743 19.81059,1.88672 19.81059,1.88672 0,0 -6.7922,14.52776 -6.60353,28.86686 0.18867,14.33909 2.45274,19.62191 2.45274,19.62191" />
     <path d="m 30.275732,127.2863 c 0,0 18.901817,1.34096 48.200862,10.32508 27.805246,8.52607 33.634316,12.94496 33.634316,12.94496" />