frontend: kanal ekleme formu

Dashboard'a name/youtubeHandle/channelId alanlarıyla bir server action
formu eklendi. Polling ve /status için channel_id gerçek bir YouTube
UC... kimliği olmalı.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/frontend/app/globals.css

@@ -91,6 +91,43 @@ th {
   margin-bottom: 1rem;
 }
 
+.add-channel-form {
+  display: flex;
+  gap: 0.5rem;
+  flex-wrap: wrap;
+}
+
+.add-channel-form input {
+  flex: 1;
+  min-width: 160px;
+  background: var(--bg);
+  border: 1px solid var(--border);
+  border-radius: 6px;
+  padding: 0.5rem 0.7rem;
+  color: var(--text);
+  font-size: 0.9rem;
+}
+
+.add-channel-form input:focus {
+  outline: none;
+  border-color: var(--accent);
+}
+
+.add-channel-form button {
+  background: var(--accent);
+  border: none;
+  border-radius: 6px;
+  padding: 0.5rem 1rem;
+  color: #fff;
+  font-weight: 600;
+  font-size: 0.9rem;
+  cursor: pointer;
+}
+
+.add-channel-form button:hover {
+  opacity: 0.9;
+}
+
 .card-head {
   display: flex;
   justify-content: space-between;