Improvements to fitness page

- Data now comes from a calendar
- Hovering in charts shows day info
- Optical enhancements to chart rendering
- Allow setting/showing goal weight
- Allow toggeling between absolute and zoomed in weight axis

assets/style.css

@@ -837,8 +837,10 @@ aside.sidebar:empty { display: none; }
    Server-rendered inline SVG charts. Geometry comes precomputed from Go;
    colors and strokes are applied here via classes so the inline SVG follows
    the theme palette. */
-.fitness-chart { padding: var(--space-3); }
+.fitness-chart { position: relative; padding: var(--space-3); }
 .fitness-chart-header { margin-bottom: var(--space-2); }
+.fitness-controls { gap: var(--space-3); }
+.fitness-absolute { display: flex; align-items: center; gap: var(--space-1); font-size: var(--font-sm); color: var(--text-muted); }
 .fitness-range { width: auto; font-size: var(--font-sm); }
 .fitness-empty {
     border: var(--border-dashed);
@@ -852,8 +854,24 @@ aside.sidebar:empty { display: none; }
 .fitness-svg .chart-label { fill: var(--text-muted); font-size: var(--font-xs); }
 .fitness-svg .chart-line { fill: none; stroke: var(--link); stroke-width: 1.5; }
 .fitness-svg .chart-dot { fill: var(--link); }
-.fitness-svg .chart-goal { stroke: var(--primary-hover); stroke-dasharray: 4 3; }
-.fitness-svg .chart-goal-label { fill: var(--primary-hover); font-size: var(--font-xs); }
+.fitness-svg.is-dense .chart-dot { display: none; }
+.fitness-svg:not(.is-hover) :is(.chart-cursor, .chart-focus) { display: none; }
+.fitness-svg .chart-cursor { stroke: var(--text-muted); stroke-dasharray: 2 2; }
+.fitness-svg .chart-focus { fill: var(--link-hover); stroke: var(--bg); stroke-width: 1.5; }
+.fitness-svg .chart-goal { stroke: var(--danger); stroke-dasharray: 4 3; }
+.fitness-svg .chart-goal-label { fill: var(--danger-hover); font-size: var(--font-xs); }
+.fitness-tip {
+    position: absolute;
+    display: flex;
+    flex-direction: column;
+    padding: var(--space-1) var(--space-2);
+    background: var(--bg);
+    border: var(--border);
+    font-size: var(--font-sm);
+    white-space: nowrap;
+    pointer-events: none;
+}
+.fitness-tip[hidden] { display: none; }
 
 /* === Responsive === */
 @media (max-width: 1100px) {