feat(gateway,cli,types): wire token usage, model info, and thinking levels

Gateway:
- Emit session:info on session creation with provider, model, thinking level
- Include SessionUsagePayload in agent:end with token stats, cost, context usage
- Handle set:thinking client event to cycle thinking levels
- Respond with updated session:info after thinking level change

Types (@mosaic/types):
- Add SessionUsagePayload (tokens, cost, context) to AgentEndPayload
- Add SessionInfoPayload (provider, model, thinking level, available levels)
- Add SetThinkingPayload and set:thinking to ClientToServerEvents
- Add session:info to ServerToClientEvents

CLI TUI:
- useSocket now tracks tokenUsage, modelName, providerName, thinkingLevel
- Updates from both session:info and agent:end usage payload
- Ctrl+T cycles thinking level via set:thinking socket event
- Footer shows thinking level next to model (e.g. 'claude-opus-4-6 • medium')
- Token stats populate with real ↑in ↓out Rcache Wcache $cost ctx%

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

@@ -10,6 +10,7 @@ export interface BottomBarProps {
   connecting: boolean;
   modelName: string | null;
   providerName: string | null;
+  thinkingLevel: string;
 }
 
 function formatTokens(n: number): string {
@@ -34,6 +35,7 @@ export function BottomBar({
   connecting,
   modelName,
   providerName,
+  thinkingLevel,
 }: BottomBarProps) {
   const gatewayStatus = connected ? 'Connected' : connecting ? 'Connecting…' : 'Disconnected';
   const gatewayColor = connected ? 'green' : connecting ? 'yellow' : 'red';
@@ -97,6 +99,7 @@ export function BottomBar({
           <Text dimColor>
             {providerName ? `(${providerName}) ` : ''}
             {modelName ?? 'awaiting model'}
+            {thinkingLevel !== 'off' ? ` • ${thinkingLevel}` : ''}
           </Text>
         </Box>
       </Box>