feat: add styles for polling app UI

Responsive single-column layout (max 480px) with styles for:
- Option items with label/vote-button rows
- Voted state highlighting (green tint)
- Active/closed timer color states
- Disabled button opacity
- Full-width copy URL button

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

styles.css

@@ -0,0 +1,93 @@
+body {
+    font-family: sans-serif;
+    max-width: 480px;
+    margin: 40px auto;
+    padding: 0 16px;
+}
+
+#add-option {
+    display: flex;
+    gap: 8px;
+    margin-bottom: 8px;
+}
+
+#option-input {
+    flex: 1;
+    padding: 8px;
+    font-size: 1rem;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+}
+
+#duplicate-msg {
+    color: #c00;
+    font-size: 0.9rem;
+    margin-bottom: 12px;
+}
+
+button {
+    padding: 8px 16px;
+    font-size: 1rem;
+    cursor: pointer;
+    border: 1px solid #ccc;
+    border-radius: 4px;
+    background: #fff;
+}
+
+button:hover:not(:disabled) {
+    background: #f0f0f0;
+}
+
+button:disabled {
+    opacity: 0.5;
+    cursor: default;
+}
+
+#timer-section {
+    display: flex;
+    align-items: center;
+    gap: 12px;
+    margin-bottom: 16px;
+}
+
+.timer.active {
+    font-weight: bold;
+    color: #1a6e1a;
+}
+
+.timer.closed {
+    font-weight: bold;
+    color: #c00;
+}
+
+.option-item {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    padding: 10px 12px;
+    border: 1px solid #ddd;
+    border-radius: 4px;
+    margin-bottom: 8px;
+}
+
+.option-label {
+    flex: 1;
+}
+
+.vote-btn {
+    padding: 4px 12px;
+    font-size: 0.9rem;
+    white-space: nowrap;
+}
+
+.vote-btn.voted {
+    background: #e6f4e6;
+    border-color: #4a9e4a;
+    color: #2a6e2a;
+}
+
+
+#copy-btn {
+    margin-top: 16px;
+    width: 100%;
+}