feat(cli): branded top bar with mosaic windmill icon

- ASCII art mosaic windmill: 4 colored tiles (blue, purple, teal, amber)
  with pink center, matching the Mosaic Stack brand
- 3-line info block (Claude Code style):
  Line 1: 'Mosaic Stack v0.0.0'
  Line 2: model (context) · thinking · agent name
  Line 3: ● host connection status
- Remove bordered box in favor of open layout with icon

packages/cli/src/tui/components/top-bar.tsx

@@ -3,18 +3,94 @@ import { Box, Text } from 'ink';
 
 export interface TopBarProps {
   gatewayUrl: string;
+  version: string;
+  modelName: string | null;
+  thinkingLevel: string;
+  contextWindow: number;
+  agentName: string;
+  connected: boolean;
+  connecting: boolean;
 }
 
-export function TopBar({ gatewayUrl }: TopBarProps) {
-  // Strip protocol for compact display
-  const host = gatewayUrl.replace(/^https?:\/\//, '');
+/** Compact the URL — strip protocol */
+function compactHost(url: string): string {
+  return url.replace(/^https?:\/\//, '');
+}
 
+function formatContextWindow(n: number): string {
+  if (n >= 1_000_000) return `${(n / 1_000_000).toFixed(0)}M`;
+  if (n >= 1_000) return `${(n / 1_000).toFixed(0)}k`;
+  return String(n);
+}
+
+/**
+ * Mosaic windmill icon — 4 colored tiles + pink center
+ * Colors from the Mosaic brand:
+ *   TL: blue (#2f80ff)  TR: purple (#8b5cf6)
+ *   BL: amber (#f59e0b) BR: teal (#14b8a6)
+ *   Center: pink (#ec4899)
+ */
+function MosaicIcon() {
   return (
-    <Box borderStyle="single" borderColor="gray" paddingX={1} justifyContent="space-between">
-      <Text bold color="blue">
-        Mosaic Stack TUI
+    <Box flexDirection="column" marginRight={1}>
+      <Text>
+        <Text color="#2f80ff">██</Text>
+        <Text> </Text>
+        <Text color="#8b5cf6">██</Text>
+      </Text>
+      <Text>
+        <Text> </Text>
+        <Text color="#ec4899">██</Text>
+        <Text> </Text>
+      </Text>
+      <Text>
+        <Text color="#f59e0b">██</Text>
+        <Text> </Text>
+        <Text color="#14b8a6">██</Text>
       </Text>
-      <Text dimColor>{host}</Text>
+    </Box>
+  );
+}
+
+export function TopBar({
+  gatewayUrl,
+  version,
+  modelName,
+  thinkingLevel,
+  contextWindow,
+  agentName,
+  connected,
+  connecting,
+}: TopBarProps) {
+  const host = compactHost(gatewayUrl);
+  const connectionIndicator = connected ? '●' : '○';
+  const connectionColor = connected ? 'green' : connecting ? 'yellow' : 'red';
+
+  // Build model description line like: "claude-opus-4-6 (1M context) · default"
+  const modelDisplay = modelName ?? 'awaiting model';
+  const contextStr = contextWindow > 0 ? ` (${formatContextWindow(contextWindow)} context)` : '';
+  const thinkingStr = thinkingLevel !== 'off' ? ` · ${thinkingLevel}` : '';
+
+  return (
+    <Box paddingX={1} paddingY={0}>
+      <MosaicIcon />
+      <Box flexDirection="column">
+        <Text>
+          <Text bold color="#56a0ff">
+            Mosaic Stack
+          </Text>
+          <Text dimColor> v{version}</Text>
+        </Text>
+        <Text dimColor>
+          {modelDisplay}
+          {contextStr}
+          {thinkingStr} · {agentName}
+        </Text>
+        <Text>
+          <Text color={connectionColor}>{connectionIndicator}</Text>
+          <Text dimColor> {host}</Text>
+        </Text>
+      </Box>
     </Box>
   );
 }