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/app.tsx

@@ -23,10 +23,22 @@ export function TuiApp({ gatewayUrl, conversationId, sessionCookie }: TuiAppProp
     initialConversationId: conversationId,
   });
 
-  useInput((_ch, key) => {
-    if (key.ctrl && _ch === 'c') {
+  useInput((ch, key) => {
+    if (key.ctrl && ch === 'c') {
       exit();
     }
+    // Ctrl+T: cycle thinking level
+    if (key.ctrl && ch === 't') {
+      const levels = socket.availableThinkingLevels;
+      if (levels.length > 0) {
+        const currentIdx = levels.indexOf(socket.thinkingLevel);
+        const nextIdx = (currentIdx + 1) % levels.length;
+        const next = levels[nextIdx];
+        if (next) {
+          socket.setThinkingLevel(next);
+        }
+      }
+    }
   });
 
   return (
@@ -54,6 +66,7 @@ export function TuiApp({ gatewayUrl, conversationId, sessionCookie }: TuiAppProp
         connecting={socket.connecting}
         modelName={socket.modelName}
         providerName={socket.providerName}
+        thinkingLevel={socket.thinkingLevel}
       />
     </Box>
   );