Added check-in to admin Participants view.

frontend/src/pages/Participants.svelte

@@ -129,6 +129,16 @@
     }
   }
 
+  async function checkInTicket(tk) {
+    error = ''
+    try {
+      const result = await api.tickets.checkIn(tk.id)
+      if (result.ticket) await db.tickets.put(result.ticket)
+    } catch (err) {
+      error = err.message
+    }
+  }
+
   function fmtTime(ts) {
     if (!ts) return ''
     return new Date(ts).toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' })
@@ -426,7 +436,7 @@
                           {#if tk.checked_in_at}
                             <span class="badge badge-checked">Checked in {fmtTime(tk.checked_in_at)}</span>
                           {:else}
-                            <span class="badge badge-unchecked">Not checked in</span>
+                            <button class="btn btn-success btn-sm" onclick={() => checkInTicket(tk)}>✓ Check in</button>
                           {/if}
                           <div class="text-muted" style="font-size:0.75rem">{tk.source}</div>
                         </div>