feat(matching): add schedule config for division collision groups

Allow event organizers to configure which divisions run in parallel
(same time slot) for accurate collision detection in the auto-matching
algorithm. Divisions in the same slot will collide with each other.

- Add scheduleConfig JSON field to Event model
- Add PUT /events/:slug/schedule-config API endpoint
- Update matching algorithm to use slot-based collision detection
- Add UI in EventDetailsPage for managing division slots
- Add unit tests for schedule-based collision detection

backend/src/routes/events.js

@@ -381,6 +381,7 @@ router.get('/:slug/details', authenticate, async (req, res, next) => {
           description: event.description,
           registrationDeadline: event.registrationDeadline,
           matchingRunAt: event.matchingRunAt,
+          scheduleConfig: event.scheduleConfig,
         },
         checkin: {
           token: checkinToken.token,
@@ -914,6 +915,76 @@ router.delete('/:slug/heats/:id', authenticate, async (req, res, next) => {
 // AUTO-MATCHING ENDPOINTS
 // ============================================
 
+// PUT /api/events/:slug/schedule-config - Set schedule configuration (division order and collision groups)
+router.put('/:slug/schedule-config', authenticate, async (req, res, next) => {
+  try {
+    const { slug } = req.params;
+    const { scheduleConfig } = req.body;
+
+    // Validate schedule config structure
+    if (scheduleConfig !== null && scheduleConfig !== undefined) {
+      if (!scheduleConfig.slots || !Array.isArray(scheduleConfig.slots)) {
+        return res.status(400).json({
+          success: false,
+          error: 'scheduleConfig must have a "slots" array',
+        });
+      }
+
+      // Validate each slot
+      for (let i = 0; i < scheduleConfig.slots.length; i++) {
+        const slot = scheduleConfig.slots[i];
+        if (typeof slot.order !== 'number' || !Array.isArray(slot.divisionIds)) {
+          return res.status(400).json({
+            success: false,
+            error: `Slot ${i} must have "order" (number) and "divisionIds" (array)`,
+          });
+        }
+
+        // Validate divisionIds are numbers
+        if (!slot.divisionIds.every(id => typeof id === 'number')) {
+          return res.status(400).json({
+            success: false,
+            error: `Slot ${i} divisionIds must be an array of numbers`,
+          });
+        }
+      }
+    }
+
+    // Find event
+    const event = await prisma.event.findUnique({
+      where: { slug },
+      select: { id: true },
+    });
+
+    if (!event) {
+      return res.status(404).json({
+        success: false,
+        error: 'Event not found',
+      });
+    }
+
+    // Update schedule config
+    const updated = await prisma.event.update({
+      where: { id: event.id },
+      data: {
+        scheduleConfig: scheduleConfig || null,
+      },
+      select: {
+        id: true,
+        slug: true,
+        scheduleConfig: true,
+      },
+    });
+
+    res.json({
+      success: true,
+      data: updated,
+    });
+  } catch (error) {
+    next(error);
+  }
+});
+
 // PUT /api/events/:slug/registration-deadline - Set registration deadline
 router.put('/:slug/registration-deadline', authenticate, async (req, res, next) => {
   try {