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/OdinThread.tsx

@@ -170,8 +170,14 @@ export default function OdinThread({
       {turns.map((t, i) => {
         const isUser = t.role === "user";
         return (
-          <Box
+          <MotionBox
             key={i}
+            initial={reduce ? { opacity: 0 } : { opacity: 0, y: 10 }}
+            animate={{ opacity: 1, y: 0 }}
+            transition={{
+              duration: reduce ? 0.3 : 0.34,
+              ease: [0.16, 1, 0.3, 1],
+            }}
             sx={{
               display: "flex",
               flexDirection: "row",
@@ -204,7 +210,7 @@ export default function OdinThread({
                 {t.content}
               </Typography>
             </Box>
-          </Box>
+          </MotionBox>
         );
       })}