feat(odin): chat animations + immersive fullscreen mobile view

- bubbles spring in anchored at their avatar corner; thinking state is a
  typing bubble (three bouncing dots) that springs in/out where the reply
  lands; reduced-motion falls back to opacity fades
- mobile /odin is immersive: AppShell hides its header and main padding
  below md, the chat owns 100svh full-bleed with safe-area insets and a
  back arrow (history back, home on deep links)
- desktop card border kept divider-colored via longhand border props (a
  responsive border shorthand reset the color to black)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/components/odin/OdinChat.tsx

@@ -1,4 +1,5 @@
 import { useState, useRef, useEffect } from "react";
+import { useNavigate } from "react-router-dom";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import Box from "@mui/material/Box";
 import Typography from "@mui/material/Typography";
@@ -109,6 +110,17 @@ export default function OdinChat() {
   });
   const [sidebarOpen, setSidebarOpen] = useState(false);
 
+  // Mobile is immersive (no AppShell header on /odin) — this is the only way
+  // back. A deep link straight to /odin has no in-app history → go home.
+  const navigate = useNavigate();
+  const goBack = () => {
+    if (((window.history.state as { idx?: number } | null)?.idx ?? 0) > 0) {
+      navigate(-1);
+    } else {
+      navigate("/");
+    }
+  };
+
   // No auto-select: like claude.ai, we land on a fresh "new chat" (activeId
   // null) and the sidebar lists existing conversations to open. A conversation
   // row in the DB is created lazily on the first message (see submit), so
@@ -424,11 +436,16 @@ export default function OdinChat() {
         // browser-chrome height. svh sizes for the bar-visible viewport — the
         // page never scrolls and the chat's message list scrolls internally.
         // Desktop: svh === vh.
-        height: "calc(100svh - 100px)",
+        // Mobile is immersive (AppShell hides its header and main padding on
+        // /odin): the chat owns the whole viewport, full-bleed.
+        height: { xs: "100svh", md: "calc(100svh - 100px)" },
         display: "flex",
-        border: 1,
+        // Longhand on purpose: a responsive `border` shorthand lands in a
+        // media query AFTER borderColor and resets the color to black.
+        borderStyle: "solid",
+        borderWidth: { xs: 0, md: 1 },
         borderColor: "divider",
-        borderRadius: 3,
+        borderRadius: { xs: 0, md: 3 },
         bgcolor: "background.paper",
         overflow: "hidden",
       }}
@@ -454,15 +471,41 @@ export default function OdinChat() {
           flexDirection: "column",
           gap: 1.5,
           p: 2,
+          // Immersive mobile: respect the notch / home-indicator insets
+          // (env() is 0 outside standalone mode, so max() keeps the 16px).
+          pt: { xs: "max(16px, env(safe-area-inset-top))", md: 2 },
+          pb: { xs: "max(16px, env(safe-area-inset-bottom))", md: 2 },
         }}
       >
         <Box sx={{ display: "flex", alignItems: "center", gap: 1 }}>
+          {isMobile && (
+            <IconButton
+              onClick={goBack}
+              aria-label="Zpět"
+              size="small"
+              sx={{ ml: -0.5, flexShrink: 0 }}
+            >
+              <Box
+                component="svg"
+                viewBox="0 0 24 24"
+                sx={{ width: 22, height: 22 }}
+                fill="none"
+                stroke="currentColor"
+                strokeWidth="2"
+                strokeLinecap="round"
+                strokeLinejoin="round"
+              >
+                <line x1="19" y1="12" x2="5" y2="12" />
+                <polyline points="12 19 5 12 12 5" />
+              </Box>
+            </IconButton>
+          )}
           {isMobile && (
             <IconButton
               onClick={() => setSidebarOpen(true)}
               aria-label="Konverzace"
               size="small"
-              sx={{ ml: -0.5, flexShrink: 0 }}
+              sx={{ flexShrink: 0 }}
             >
               <Box
                 component="svg"