add suport for browser context transport

Author: AdirD

src/BROWSER_CONTEXT_TRANSPORT_README.md

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+# BrowserContextTransport
+
+Enables communication between different browser contexts using the MessageChannel API.
+
+## Motivation
+
+When building agentic chat applications in the browser with MCP, you need a reliable way for components to communicate across browser security boundaries. For example:
+
+- Chat UI running in a sandboxed iframe needs to talk to MCP clients/servers
+- Agent tools executing in web workers need to communicate with the main thread
+- Security-sensitive components isolated in separate contexts need to exchange messages
+
+Other transports don't work well for these browser scenarios:
+- **InMemoryTransport**: Can't cross browser context boundaries (iframes, workers)
+- **WebSocketTransport**: Requires network connection, server infrastructure, and adds latency
+- **SSETransport**: Limited to one-way communication, requires network connection
+
+## Use Case
+
+```mermaid
+flowchart LR
+    subgraph Browser["Browser"]
+        subgraph IFrame["Iframe"]
+            ChatUI["UI"] --> Client["Client"]
+            Client --> Transport["Transport"]
+        end
+        Transport --> Server["Server"]
+        Server --> AppLogic["App"]
+    end
+    
+    classDef component fill:#e1f5fe,stroke:#01579b,stroke-width:1px,rx:5px,ry:5px;
+    classDef container fill:#f5f5f5,stroke:#333,stroke-width:1px;
+    class Client,Server,AppLogic,ChatUI,Transport component;
+```
+
+## Quick Start
+
+### Creating a Transport Pair
+
+Most basic use case - both ends in same context:
+
+```typescript
+const [clientTransport, serverTransport] = BrowserContextTransport.createChannelPair();
+const client = new Client(clientTransport);
+const server = new Server(serverTransport);
+```
+
+### With Iframes
+
+Special code is needed for iframes because they're separate JavaScript execution contexts with their own memory space. You must use `postMessage` to transfer a `MessagePort`:
+
+```typescript
+// Parent window
+const iframe = document.getElementById('myIframe');
+const channel = new MessageChannel();
+const clientTransport = new BrowserContextTransport(channel.port1);
+const client = new Client(clientTransport);
+iframe.contentWindow.postMessage('init', '*', [channel.port2]);
+
+// Inside iframe
+window.addEventListener('message', (event) => {
+  if (event.data === 'init' && event.ports[0]) {
+    const serverTransport = new BrowserContextTransport(event.ports[0]);
+    const server = new Server(serverTransport);
+  }
+});
+```
+
+### With Workers
+
+Workers also require special handling since they run in isolated threads. Like iframes, they need a `MessagePort` transferred via `postMessage`:
+
+```typescript
+// Main thread
+const worker = new Worker('worker.js');
+const channel = new MessageChannel();
+const clientTransport = new BrowserContextTransport(channel.port1);
+worker.postMessage('init', [channel.port2]);
+
+// In worker
+self.addEventListener('message', (event) => {
+  if (event.data === 'init') {
+    const serverTransport = new BrowserContextTransport(event.ports[0]);
+    const server = new Server(serverTransport);
+  }
+});
+```