fix: DM message ordering, consolidate input toolbar, add rich text/WYSIWYG, file upload with drag-drop

- Fix DM backend ListMessages to use DESC + reverse (match channel handler)
- Remove spurious .reverse() from frontend message/conversation stores
- Create shared MessageInput component with Slack-style single toolbar row
- Add file upload via + button with progress bar and drag-and-drop
- Add markdown/rich text toggle with full WYSIWYG block formatting
  (lists, blockquotes, links, headings, code blocks)
- Add frontend+backend security for file uploads (extension + content-type guards)

web/package.json

@@ -10,6 +10,9 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@fortawesome/fontawesome-svg-core": "^7.3.0",
+    "@fortawesome/free-solid-svg-icons": "^7.3.0",
+    "@fortawesome/react-fontawesome": "^3.3.1",
     "@livekit/components-react": "^2.9.21",
     "@livekit/track-processors": "^0.7.2",
     "emoji-picker-react": "^4.19.1",