MCP process leak: chrome-devtools-mcp and tavily-mcp cause memory explosion

## Problem Description

After updating CoPaw, the system has a serious process leak issue. The `node.exe` process count grows from normal to 40+ processes, each taking 75-130 MB memory, consuming several GB of RAM.

## Reproduction Steps

1. Run CoPaw with multiple agents
2. Use any MCP functionality (chrome-devtools-mcp, tavily-mcp)
3. Observe task manager - node.exe processes keep growing

## Log Analysis

CoPaw logs show MCP clients frequently disconnecting and reconnecting:

```
MCP client 'tavily_mcp' session interrupted while listing tools; trying recovery
Stopping MCP client: tavily_mcp
MCP client lifecycle task exited: tavily_mcp
MCP client connected: tavily_mcp
```

Each reconnect starts new watchdog child processes from `chrome-devtools-mcp`, but old processes are not properly terminated, causing accumulation.

## Environment

- CoPaw version: Latest
- Node.js: v22.10.0
- MCP plugins:
- chrome-devtools-mcp@0.2.6
- tavily-mcp (latest)
- Agent count: 8 (default, code_agent, data_agent, research_agent, router_agent, writer_agent, kids_english_translator, CoPaw_QA_Agent)

## Temporary Workaround

Manually terminate leaking processes:
```bash
wmic process where "name='node.exe' and CommandLine like '%%chrome-devtools%%'" call terminate
wmic process where "name='node.exe' and CommandLine like '%%tavily%%'" call terminate
```

## Expected Behavior

MCP processes should be properly cleaned up when connections close, no process accumulation should occur.

## Impact

- System RAM exhausted
- CPU usage abnormally high
- CoPaw runs slowly or freezes