Revert "feat: AI entry button at the cell's bottom-right + clear input after success"

This reverts commit fd30e53e25.

style/base.css

@@ -4,31 +4,29 @@
     https://jupyterlab.readthedocs.io/en/stable/developer/css.html
 */
 
-/* AI entry button: rendered as a floating pill at the bottom-right
-   corner of the cell. The widget that owns it (opencode-cell-actions)
-   is registered in the native cell toolbar but its own node is
-   display:none — only this floating button is visible. */
-.opencode-cell-ai-btn {
-  position: absolute;
-  bottom: 4px;
-  right: 4px;
-  z-index: 10;
-  border: 1px solid var(--jp-border-color1, #999);
-  background: var(--jp-layout-color1, #fff);
-  color: var(--jp-ui-font-color1, #333);
-  padding: 1px 8px;
-  border-radius: 10px;
-  font-size: var(--jp-ui-font-size0, 11px);
-  line-height: 1.3;
+/* Single AI action button inside the native Cell toolbar (active cell, top-right). */
+.opencode-cell-actions {
+  display: flex;
+  align-items: center;
+}
+
+.opencode-cell-actions .opencode-btn {
+  border: none;
+  background: transparent;
+  padding: 0 6px;
+  font-size: var(--jp-ui-font-size1);
+  line-height: 20px;
   cursor: pointer;
+  white-space: nowrap;
 }
 
-.opencode-cell-ai-btn:hover {
-  background: var(--jp-layout-color2, #f0f0f0);
+.opencode-cell-actions .opencode-btn:hover:enabled {
+  background: var(--jp-layout-color2);
+  border-radius: 2px;
 }
 
-.opencode-cell-ai-btn:disabled {
-  opacity: 0.5;
+.opencode-cell-actions .opencode-btn:disabled {
+  opacity: 0.4;
   cursor: default;
 }