refactor: replace any types with proper TypeScript types across gateway client, hooks, and components

- Add GatewayMessage and JsonPayload interfaces to gateway.ts
- Type WebSocket message parsing with GatewayMessage instead of any
- Use ReturnType<typeof setTimeout> for timer refs
- Type chat event payload destructuring explicitly
- Add ChatPayloadMessage interface for extractText()
- Replace any casts in loadSessions/loadHistory with typed assertions
- Add str() helper in ToolCall.tsx for safe unknown→string extraction
- Use Extract<MessageBlock, ...> type guards instead of `as any` casts
- Type CodeBlock children prop properly

src/components/CodeBlock.tsx

@@ -10,7 +10,7 @@ export function CodeBlock(props: HTMLAttributes<HTMLPreElement>) {
 
   const handleCopy = useCallback(() => {
     // Extract text from the nested <code> element
-    const code = (props.children as any)?.props?.children;
+    const code = (props.children as React.ReactElement<{ children?: string }> | undefined)?.props?.children;
     if (typeof code === 'string') {
       navigator.clipboard.writeText(code).then(() => {
         setCopied(true);