fitness: disable chart grow-in animation, add trendlines to exercise charts

Disable initial animation on all Chart.js charts (FitnessChart and
cospend BarChart) while keeping transition animations for interactions.
Add linear regression trendline with ±1σ uncertainty bands to exercise
charts (Est. 1RM, Max Weight, Total Volume).

src/lib/components/cospend/BarChart.svelte

@@ -107,6 +107,7 @@
       options: {
         responsive: true,
         maintainAspectRatio: false,
+        animation: { duration: 0 },
         layout: {
           padding: {
             top: 40
@@ -322,6 +323,15 @@
 
   onMount(() => {
     createChart();
+    // Enable animations for subsequent updates (legend toggles, etc.)
+    requestAnimationFrame(() => {
+      if (chart) {
+        chart.options.animation = { duration: 300 };
+        chart.options.transitions = {
+          active: { animation: { duration: 200 } }
+        };
+      }
+    });
 
     // Watch for theme changes (both media query and data-theme attribute)
     const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');

src/lib/components/fitness/FitnessChart.svelte

@@ -69,7 +69,7 @@
 			options: {
 				responsive: true,
 				maintainAspectRatio: false,
-				animation: false,
+				animation: { duration: 0 },
 				scales: {
 					x: {
 						grid: { display: false },
@@ -120,6 +120,14 @@
 
 	onMount(() => {
 		createChart();
+		requestAnimationFrame(() => {
+			if (chart) {
+				chart.options.animation = { duration: 300 };
+				chart.options.transitions = {
+					active: { animation: { duration: 200 } }
+				};
+			}
+		});
 
 		const mq = window.matchMedia('(prefers-color-scheme: dark)');
 		const onTheme = () => setTimeout(createChart, 100);