fix(messaging-ui): reaction picker opens downward, no longer clips

The emoji picker used bottom:100% and was clipped by the message list's
overflow when reacting to a message near the top (and could spill past the
right edge). Open it downward + edge-anchored (right for others' messages,
left for my own) with width:max-content so all emojis stay visible.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-messaging-ui/src/styles.css

@@ -198,8 +198,11 @@
 }
 .miu-react-picker {
   position: absolute;
-  bottom: 100%;
+  /* Open downward + right-aligned so it never clips against the top of the scroll area
-  margin-bottom: 4px;
+     (the reported bug) or spills past the right edge. */
+  top: 100%;
+  right: 0;
+  margin-top: 4px;
   display: flex;
   gap: 2px;
   padding: 4px;
@@ -208,6 +211,12 @@
   background: var(--miu-panel);
   box-shadow: 0 6px 20px rgba(0, 0, 0, 0.4);
   z-index: 5;
+  width: max-content;
+}
+/* On my own (right-aligned) messages, anchor the picker to the left instead so it stays in view. */
+.miu-msg.is-mine .miu-react-picker {
+  right: auto;
+  left: 0;
 }
 .miu-react-emoji {
   border: none;