Enhance logout to clear MCP OAuth tokens and disconnect all servers

## Problem
The logout button only cleared inference provider authentication, leaving
MCP OAuth tokens and server connections active. Users remained authenticated
to MCP servers after logging out.

## Solution
- **Clear MCP OAuth tokens**: Remove OAuth tokens and state for all MCP connections
- **Disconnect all servers**: Remove all MCP server connections on logout
- **Complete cleanup**: Comprehensive logout that clears all authentication state
- **Enhanced confirmation**: Updated dialog to inform users about MCP disconnection

## Technical Implementation
- Added MCP context integration to access connections and removal methods
- Clear OAuth tokens from localStorage for each OAuth-enabled connection
- Remove all MCP servers to properly disconnect and clean up connections
- Maintained existing inference provider logout functionality

## User Experience
- ✅ **Complete logout**: All authentication state cleared (inference + MCP)
- ✅ **Clean slate**: No residual authentication data after logout
- ✅ **Clear communication**: User informed about full scope of logout action
- ✅ **Security**: No orphaned authentication tokens left behind

## Data Cleared on Logout
- Inference provider API keys and OAuth tokens
- MCP OAuth tokens and authentication state
- Model selection preferences
- All active MCP server connections

Note: Conversation history remains intact as it's stored separately from auth data.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/components/ConversationSidebar.tsx

@@ -2,6 +2,7 @@
 
 import { useConversation } from '@/contexts/ConversationContext';
 import { useInference } from '@/contexts/InferenceContext';
+import { useMCP } from '@/contexts/MCPContext';
 
 export function ConversationSidebar() {
   const {
@@ -13,14 +14,30 @@ export function ConversationSidebar() {
   } = useConversation();
   
   const { clearProvider, provider } = useInference();
+  const { connections, removeMcpServer } = useMCP();
 
   const handleNewConversation = () => {
     createConversation();
   };
 
   const handleLogout = () => {
-    if (confirm('Are you sure you want to log out?')) {
+    if (confirm('Are you sure you want to log out? This will disconnect all MCP servers and clear your authentication.')) {
+      // Clear inference provider authentication
       clearProvider();
+      
+      // Clear MCP OAuth tokens for all connections
+      connections.forEach(connection => {
+        if (connection.authType === 'oauth') {
+          // Clear OAuth tokens and state for this connection
+          localStorage.removeItem(`mcp_oauth_tokens_${connection.id}`);
+          localStorage.removeItem(`mcp_oauth_state_${connection.id}`);
+        }
+      });
+      
+      // Remove all MCP servers (this will disconnect them)
+      connections.forEach(connection => {
+        removeMcpServer(connection.id);
+      });
     }
   };