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/types/src/chat/events.ts

@@ -9,6 +9,26 @@ export interface AgentStartPayload {
 
 export interface AgentEndPayload {
   conversationId: string;
+  usage?: SessionUsagePayload;
+}
+
+/** Session metadata emitted with agent:end and on session:info */
+export interface SessionUsagePayload {
+  provider: string;
+  modelId: string;
+  thinkingLevel: string;
+  tokens: {
+    input: number;
+    output: number;
+    cacheRead: number;
+    cacheWrite: number;
+    total: number;
+  };
+  cost: number;
+  context: {
+    percent: number | null;
+    window: number;
+  };
 }
 
 export interface AgentTextPayload {
@@ -44,6 +64,21 @@ export interface ChatMessagePayload {
   content: string;
 }
 
+/** Session info pushed when session is created or model changes */
+export interface SessionInfoPayload {
+  conversationId: string;
+  provider: string;
+  modelId: string;
+  thinkingLevel: string;
+  availableThinkingLevels: string[];
+}
+
+/** Client request to change thinking level */
+export interface SetThinkingPayload {
+  conversationId: string;
+  level: string;
+}
+
 /** Socket.IO typed event map: server → client */
 export interface ServerToClientEvents {
   'message:ack': (payload: MessageAckPayload) => void;
@@ -53,10 +88,12 @@ export interface ServerToClientEvents {
   'agent:thinking': (payload: AgentThinkingPayload) => void;
   'agent:tool:start': (payload: ToolStartPayload) => void;
   'agent:tool:end': (payload: ToolEndPayload) => void;
+  'session:info': (payload: SessionInfoPayload) => void;
   error: (payload: ErrorPayload) => void;
 }
 
 /** Socket.IO typed event map: client → server */
 export interface ClientToServerEvents {
   message: (data: ChatMessagePayload) => void;
+  'set:thinking': (data: SetThinkingPayload) => void;
 }

packages/types/src/chat/index.ts

@@ -7,6 +7,9 @@ export type {
   AgentThinkingPayload,
   ToolStartPayload,
   ToolEndPayload,
+  SessionUsagePayload,
+  SessionInfoPayload,
+  SetThinkingPayload,
   ErrorPayload,
   ChatMessagePayload,
   ServerToClientEvents,