server : (webui) revamp the input area, plus many small UI improvements (#13365)

* rework the input area

* process selected file

* change all icons to heroicons

* fix thought process collapse

* move conversation more menu to sidebar

* sun icon --> moon icon

* rm default system message

* stricter upload file check, only allow image if server has mtmd

* build it

* add renaming

* better autoscroll

* build

* add conversation group

* fix scroll

* extra context first, then user input in the end

* fix <hr> tag

* clean up a bit

* build

* add mb-3 for <pre>

* throttle adjustTextareaHeight to make it less laggy

* (nits) missing padding in sidebar

* rm stray console log

tools/server/webui/package.json

@@ -24,6 +24,8 @@
     "postcss": "^8.4.49",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
+    "react-dropzone": "^14.3.8",
+    "react-hot-toast": "^2.5.2",
     "react-markdown": "^9.0.3",
     "react-router": "^7.1.5",
     "rehype-highlight": "^7.0.2",