Fix seatmap slot matching and update member modal layout

backend/app/main.py

@@ -1308,11 +1308,59 @@ def build_center_chair_viewer_html(layout: dict[str, object]) -> str:
         ctx.lineWidth = (selected ? 2.6 : active ? 2.0 : 1.6) / camera.scale;""",
         1,
     )
+    html = html.replace(
+        """      sorted.forEach((chair, index) => {
+        chair.key = String(index + 1);
+        chair.seatNo = index + 1;
+      });""",
+        """      sorted.forEach((chair, index) => {
+        chair.seatNo = index + 1;
+      });""",
+        1,
+    )
     html = html.replace(
         "function persistPlaced() {\n      localStorage.setItem(STORAGE_KEY, JSON.stringify([...placed]));\n    }",
         "function persistPlaced() {\n      return;\n    }",
         1,
     )
+    html = html.replace(
+        """    window.addEventListener("pointerup", (event) => {
+      if (dragging && dragStart) {
+        const move = Math.hypot(event.clientX - dragStart.x, event.clientY - dragStart.y);
+        if (move < 4) {
+          const rect = canvas.getBoundingClientRect();
+          const picked = pickChair(event.clientX - rect.left, event.clientY - rect.top);
+          if (picked) {
+            if (placed.has(picked.key)) placed.delete(picked.key);
+            else placed.add(picked.key);
+            persistPlaced();
+            if (activePersonId) {
+              const currentChair = getChairByPerson(activePersonId);
+              if (chairAssignments[picked.key] === activePersonId) {
+                delete chairAssignments[picked.key];
+              } else {
+                if (currentChair && currentChair !== picked.key) delete chairAssignments[currentChair];
+                chairAssignments[picked.key] = activePersonId;
+              }
+              persistAssignments();
+              renderPeopleList();
+            }
+          }
+        }
+      }
+      dragging = false;
+      dragStart = null;
+      canvas.classList.remove("dragging");
+      requestDraw();
+    });""",
+        """    window.addEventListener("pointerup", () => {
+      dragging = false;
+      dragStart = null;
+      canvas.classList.remove("dragging");
+      requestDraw();
+    });""",
+        1,
+    )
     html = html.replace(
         """    window.addEventListener("pointerup", (event) => {
       if (dragging && dragStart) {