fix(dm): Improve DM UI consistency and fix conversation merging

- Fix duplicate conversations in dropdown by merging pk_ and name_ IDs
- Add intelligent refresh (only reload when new messages arrive)
- Fix message alignment (own messages right, others left)
- Change sent message status from 'timeout' to 'pending'
- Add emoji picker button to DM page
- Change message limit from 200 to 140 bytes (consistent with channels)
- Update README.md with corrected DM documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/static/css/style.css

@@ -362,6 +362,13 @@ main {
     background-color: #fafafa;
 }
 
+/* DM Messages List (flex container for message alignment) */
+#dmMessagesList {
+    display: flex;
+    flex-direction: column;
+    gap: 0.5rem;
+}
+
 @media (max-width: 576px) {
     .dm-messages-container {
         height: calc(100vh - 200px);