fitness: fix duration display treating minutes as seconds

The DB stores duration in minutes but formatDuration was dividing
by 3600/60 as if receiving seconds, always showing 0m.

src/lib/components/fitness/SessionCard.svelte

@@ -20,10 +20,10 @@
 	 */
 	let { session } = $props();
 
-	/** @param {number} secs */
-	function formatDuration(secs) {
-		const h = Math.floor(secs / 3600);
-		const m = Math.floor((secs % 3600) / 60);
+	/** @param {number} mins */
+	function formatDuration(mins) {
+		const h = Math.floor(mins / 60);
+		const m = mins % 60;
 		if (h > 0) return `${h}h ${m}m`;
 		return `${m}m`;
 	}

src/routes/fitness/history/[id]/+page.svelte

@@ -9,10 +9,10 @@
 	const session = $derived(data.session);
 	let deleting = $state(false);
 
-	/** @param {number} secs */
-	function formatDuration(secs) {
-		const h = Math.floor(secs / 3600);
-		const m = Math.floor((secs % 3600) / 60);
+	/** @param {number} mins */
+	function formatDuration(mins) {
+		const h = Math.floor(mins / 60);
+		const m = mins % 60;
 		if (h > 0) return `${h}h ${m}m`;
 		return `${m}m`;
 	}