feat(odin): big claude.ai-style hero on the new-conversation screen

Replace the small empty-state with a large centred hero — the animated Odin
mark + a big gradient "Odin" wordmark (responsive clamp font) and the helper
line beneath.

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

src/admin/components/odin/OdinThread.tsx

@@ -79,15 +79,34 @@ export default function OdinThread({
             flexDirection: "column",
             alignItems: "center",
             justifyContent: "center",
-            gap: 1.5,
+            gap: 2.5,
             textAlign: "center",
             px: 2,
           }}
         >
-          <OdinMark size={56} />
-          <Typography variant="body2" sx={{ color: "text.secondary" }}>
-            Dobrý den, jsem Odin. Zeptejte se, nebo přiložte fakturu (PDF) k
-            importu.
+          <Box sx={{ display: "flex", alignItems: "center", gap: 2 }}>
+            <OdinMark size={52} />
+            <Box
+              component="span"
+              sx={(t) => ({
+                fontSize: "clamp(2rem, 1.2rem + 2.4vw, 2.75rem)",
+                fontWeight: 700,
+                lineHeight: 1.1,
+                letterSpacing: "-0.02em",
+                backgroundImage: `linear-gradient(120deg, ${t.vars!.palette.primary.light}, ${t.vars!.palette.primary.main})`,
+                WebkitBackgroundClip: "text",
+                backgroundClip: "text",
+                WebkitTextFillColor: "transparent",
+              })}
+            >
+              Odin
+            </Box>
+          </Box>
+          <Typography
+            variant="body2"
+            sx={{ color: "text.secondary", maxWidth: 440 }}
+          >
+            Zeptejte se, nebo přiložte fakturu (PDF) k automatickému importu.
           </Typography>
         </Box>
       )}