Add Buy Me a Coffee support card to Admin page

Adds a styled donation card at the top of the Admin page linking to the
Buy Me a Coffee page, with a short description encouraging support.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/AdminView.vue

@@ -4,6 +4,22 @@
     <main class="container">
       <h1>Admin</h1>
 
+      <!-- Support section -->
+      <section class="section">
+        <div class="support-card">
+          <div class="support-text">
+            <div class="support-title">Enjoying Homeschool Dashboard?</div>
+            <div class="support-hint">This app is free and open source. If it's been helpful, a small donation helps cover server costs and keeps development going.</div>
+          </div>
+          <a
+            href="https://www.buymeacoffee.com/CHNS"
+            target="_blank"
+            rel="noopener noreferrer"
+            class="bmc-btn"
+          >🎉 Buy me an energy drink</a>
+        </div>
+      </section>
+
       <!-- Children section -->
       <section class="section">
         <div class="section-header">
@@ -894,6 +910,36 @@ h2 { font-size: 1.1rem; color: #94a3b8; text-transform: uppercase; letter-spacin
 .routine-hint { font-size: 0.82rem; color: #64748b; margin-bottom: 1rem; }
 .empty-small { color: #64748b; font-size: 0.9rem; padding: 1rem 0; }
 
+.support-card {
+  background: #1e293b;
+  border-radius: 1rem;
+  padding: 1.25rem 1.5rem;
+  display: flex;
+  align-items: center;
+  gap: 2rem;
+  flex-wrap: wrap;
+}
+.support-text { flex: 1; min-width: 200px; }
+.bmc-btn {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0.6rem 1.25rem;
+  background: #5F7FFF;
+  color: #fff;
+  border: 2px solid #000;
+  border-radius: 0.6rem;
+  font-size: 0.95rem;
+  font-weight: 600;
+  text-decoration: none;
+  white-space: nowrap;
+  transition: opacity 0.2s;
+  flex-shrink: 0;
+}
+.bmc-btn:hover { opacity: 0.85; }
+.support-title { font-size: 0.95rem; font-weight: 500; margin-bottom: 0.3rem; }
+.support-hint { font-size: 0.8rem; color: #64748b; line-height: 1.5; }
+
 .settings-card {
   background: #1e293b;
   border-radius: 1rem;