fitness: fix type errors, hydration warning, and add gym link

- Add exerciseId to WorkoutSession model (interface + schema)
- Fix button-in-button hydration warning in TemplateCard (use div)
- Expand FitnessChart dataset type to include all Chart.js properties
- Fix getTime type error in session update with proper cast
- Fix weight nullable type in profile stats with non-null assertion
- Fix $or query typing in templates list endpoint
- Re-add gym link on homepage pointing to /fitness

src/routes/api/fitness/sessions/[id]/+server.ts

@@ -64,7 +64,7 @@ export const PUT: RequestHandler = async ({ params, request, locals }) => {
 
     // Calculate duration if both times are provided
     if (updateData.startTime && updateData.endTime) {
-      updateData.duration = Math.round((updateData.endTime.getTime() - updateData.startTime.getTime()) / (1000 * 60));
+      updateData.duration = Math.round(((updateData.endTime as Date).getTime() - (updateData.startTime as Date).getTime()) / (1000 * 60));
     }
 
     const workoutSession = await WorkoutSession.findOneAndUpdate(

src/routes/api/fitness/stats/profile/+server.ts

@@ -88,8 +88,8 @@ export const GET: RequestHandler = async ({ locals }) => {
 		weightChart.labels.push(
 			d.toLocaleDateString('en', { month: 'short', day: 'numeric' })
 		);
-		weightChart.data.push(m.weight);
-		weights.push(m.weight);
+		weightChart.data.push(m.weight!);
+		weights.push(m.weight!);
 	}
 
 	// Adaptive window: 7 if enough data, otherwise half the data (min 2)

src/routes/api/fitness/templates/+server.ts

@@ -15,16 +15,16 @@ export const GET: RequestHandler = async ({ url, locals }) => {
     
     const includePublic = url.searchParams.get('include_public') === 'true';
     
-    let query: Record<string, unknown> = {
-      $or: [
-        { createdBy: session.user.nickname }
-      ]
-    };
+    const orConditions: Record<string, unknown>[] = [
+      { createdBy: session.user.nickname }
+    ];
 
     if (includePublic) {
-      query.$or.push({ isPublic: true });
+      orConditions.push({ isPublic: true });
     }
 
+    const query = { $or: orConditions };
+
     const templates = await WorkoutTemplate.find(query).sort({ updatedAt: -1 });
     
     return json({ templates });