feat(odin): mobile composer + responsive sidebar + message-entrance animation

- Composer rebuilt claude-style: a rounded pill with a multiline auto-growing
  textarea and attach/send ICON buttons (vertically centered), so there's room
  to type on mobile (was squeezed between two text buttons).
- Conversation list collapses into a slide-in Drawer below md, with a menu
  button in the chat header; chat is full-width on mobile.
- Each new message bubble animates in (fade + slide-up; fade-only under
  prefers-reduced-motion) via framer-motion, so sent messages and Odin's
  replies appear smoothly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/components/odin/OdinSidebar.tsx

@@ -65,7 +65,7 @@ export default function OdinSidebar({
   return (
     <Box
       sx={{
-        width: { xs: 184, sm: 232, md: 264 },
+        width: { xs: 280, md: 264 },
         flexShrink: 0,
         height: "100%",
         display: "flex",