feat: Improve UI layout and navigation

- Increase logo size (48x48 desktop, 56x56 mobile) for better visibility
- Add logo as favicon
- Add logo to mobile header
- Move user menu to navigation bars (sidebar on desktop, bottom bar on mobile)
- Fix desktop chat layout - container structure prevents voice controls cutoff
- Fix mobile bottom bar - use icon-only ActionIcons instead of truncated text buttons
- Hide Create Node/New Conversation buttons on mobile to save header space
- Make fixed header and voice controls work properly with containers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

components/Navigation/MobileBottomBar.tsx

@@ -0,0 +1,95 @@
+'use client';
+
+/**
+ * Mobile Bottom Bar Navigation
+ *
+ * Fixed bottom navigation for mobile devices (< 768px).
+ * Shows three buttons: Convo, Edit, Galaxy
+ * Highlights the active mode based on app state machine.
+ */
+
+import { Group, Button, Paper, ActionIcon, Box } from '@mantine/core';
+import { IconMessageCircle, IconEdit, IconUniverse, IconUser } from '@tabler/icons-react';
+import { useSelector } from '@xstate/react';
+import { useAppMachine } from '@/hooks/useAppMachine';
+import { UserMenu } from '@/components/UserMenu';
+
+export function MobileBottomBar() {
+  const actor = useAppMachine();
+  const state = useSelector(actor, (state) => state);
+  const send = actor.send;
+
+  const handleNavigation = (target: 'convo' | 'edit' | 'galaxy') => {
+    console.log('[Mobile Nav] Navigating to:', target);
+
+    if (target === 'convo') {
+      send({ type: 'NAVIGATE_TO_CONVO' });
+    } else if (target === 'edit') {
+      send({ type: 'NAVIGATE_TO_EDIT' });
+    } else if (target === 'galaxy') {
+      send({ type: 'NAVIGATE_TO_GALAXY' });
+    }
+  };
+
+  const isConvo = state.matches('convo');
+  const isEdit = state.matches('edit');
+  const isGalaxy = state.matches('galaxy');
+
+  console.log('[Mobile Nav] Current state:', state.value, {
+    isConvo,
+    isEdit,
+    isGalaxy,
+  });
+
+  return (
+    <Paper
+      withBorder
+      p="md"
+      radius={0}
+      style={{
+        position: 'fixed',
+        bottom: 0,
+        left: 0,
+        right: 0,
+        zIndex: 100,
+        borderTop: '1px solid #dee2e6',
+      }}
+    >
+      <Group justify="space-around" grow>
+        <ActionIcon
+          variant={isConvo ? 'filled' : 'subtle'}
+          color={isConvo ? 'blue' : 'gray'}
+          onClick={() => handleNavigation('convo')}
+          size={48}
+          radius="md"
+        >
+          <IconMessageCircle size={24} />
+        </ActionIcon>
+
+        <ActionIcon
+          variant={isEdit ? 'filled' : 'subtle'}
+          color={isEdit ? 'blue' : 'gray'}
+          onClick={() => handleNavigation('edit')}
+          size={48}
+          radius="md"
+        >
+          <IconEdit size={24} />
+        </ActionIcon>
+
+        <ActionIcon
+          variant={isGalaxy ? 'filled' : 'subtle'}
+          color={isGalaxy ? 'blue' : 'gray'}
+          onClick={() => handleNavigation('galaxy')}
+          size={48}
+          radius="md"
+        >
+          <IconUniverse size={24} />
+        </ActionIcon>
+
+        <Box style={{ display: 'flex', alignItems: 'center', justifyContent: 'center' }}>
+          <UserMenu />
+        </Box>
+      </Group>
+    </Paper>
+  );
+}